-@c Copyright (C) 1988,1989,1992,1993,1994,1996,1998,1999,2000,2001,2002,
-@c 2003 Free Software Foundation, Inc.
+@c Copyright (C) 1988,1989,1992,1993,1994,1996,1998,1999,2000,2001,2002,2003,2004
+@c Free Software Foundation, Inc.
@c This is part of the GCC manual.
@c For copying conditions, see the file gcc.texi.
@itemize @bullet
@item
-When used as part of the register variable extension, see
+When used as part of the register variable extension, see
@ref{Explicit Reg Vars}.
@item
@menu
* Statement Exprs:: Putting statements and declarations inside expressions.
-* Local Labels:: Labels local to a statement-expression.
+* Local Labels:: Labels local to a block.
* Labels as Values:: Getting pointers to labels, and computed gotos.
* Nested Functions:: As in Algol and Pascal, lexical scoping of functions.
* Constructing Calls:: Dispatching a call to another function.
* Typeof:: @code{typeof}: referring to the type of an expression.
-* Lvalues:: Using @samp{?:}, @samp{,} and casts in lvalues.
* Conditionals:: Omitting the middle operand of a @samp{?:} expression.
* Long Long:: Double-word integers---@code{long long int}.
* Complex:: Data types for complex numbers.
* Hex Floats:: Hexadecimal floating-point constants.
* Zero Length:: Zero-length arrays.
* Variable Length:: Arrays whose length is computed at run time.
+* Empty Structures:: Structures with no members.
* Variadic Macros:: Macros with a variable number of arguments.
* Escaped Newlines:: Slightly looser rules for escaped newlines.
-* Multi-line Strings:: String literals with embedded newlines.
* Subscripting:: Any array can be subscripted, even if not an lvalue.
* Pointer Arith:: Arithmetic on @code{void}-pointers and function pointers.
* Initializers:: Non-constant initializers.
by braces; in this construct, parentheses go around the braces. For
example:
-@example
+@smallexample
(@{ int y = foo (); int z;
if (y > 0) z = y;
else z = - y;
z; @})
-@end example
+@end smallexample
@noindent
is a valid (though slightly more complex than necessary) expression
``maximum'' function is commonly defined as a macro in standard C as
follows:
-@example
+@smallexample
#define max(a,b) ((a) > (b) ? (a) : (b))
-@end example
+@end smallexample
@noindent
@cindex side effects, macro argument
type of the operands (here let's assume @code{int}), you can define
the macro safely as follows:
-@example
+@smallexample
#define maxint(a,b) \
(@{int _a = (a), _b = (b); _a > _b ? _a : _b; @})
-@end example
+@end smallexample
Embedded statements are not allowed in constant expressions, such as
the value of an enumeration constant, the width of a bit-field, or
If you don't know the type of the operand, you can still do this, but you
must use @code{typeof} (@pxref{Typeof}).
-Statement expressions are not supported fully in G++, and their fate
-there is unclear. (It is possible that they will become fully supported
-at some point, or that they will be deprecated, or that the bugs that
-are present will continue to exist indefinitely.) Presently, statement
-expressions do not work well as default arguments.
+In G++, the result value of a statement expression undergoes array and
+function pointer decay, and is returned by value to the enclosing
+expression. For instance, if @code{A} is a class, then
-In addition, there are semantic issues with statement-expressions in
-C++. If you try to use statement-expressions instead of inline
-functions in C++, you may be surprised at the way object destruction is
-handled. For example:
+@smallexample
+ A a;
-@example
-#define foo(a) (@{int b = (a); b + 3; @})
-@end example
+ (@{a;@}).Foo ()
+@end smallexample
@noindent
-does not work the same way as:
+will construct a temporary @code{A} object to hold the result of the
+statement expression, and that will be used to invoke @code{Foo}.
+Therefore the @code{this} pointer observed by @code{Foo} will not be the
+address of @code{a}.
+
+Any temporaries created within a statement within a statement expression
+will be destroyed at the statement's end. This makes statement
+expressions inside macros slightly different from function calls. In
+the latter case temporaries introduced during argument evaluation will
+be destroyed at the end of the statement that includes the function
+call. In the statement expression case they will be destroyed during
+the statement expression. For instance,
-@example
-inline int foo(int a) @{ int b = a; return b + 3; @}
-@end example
+@smallexample
+#define macro(a) (@{__typeof__(a) b = (a); b + 3; @})
+template<typename T> T function(T a) @{ T b = a; return b + 3; @}
+
+void foo ()
+@{
+ macro (X ());
+ function (X ());
+@}
+@end smallexample
@noindent
-In particular, if the expression passed into @code{foo} involves the
-creation of temporaries, the destructors for those temporaries will be
-run earlier in the case of the macro than in the case of the function.
+will have different places where temporaries are destroyed. For the
+@code{macro} case, the temporary @code{X} will be destroyed just after
+the initialization of @code{b}. In the @code{function} case that
+temporary will be destroyed when the function returns.
These considerations mean that it is probably a bad idea to use
statement-expressions of this form in header files that are designed to
@cindex local labels
@cindex macros, local labels
-Each statement expression is a scope in which @dfn{local labels} can be
-declared. A local label is simply an identifier; you can jump to it
-with an ordinary @code{goto} statement, but only from within the
-statement expression it belongs to.
+GCC allows you to declare @dfn{local labels} in any nested block
+scope. A local label is just like an ordinary label, but you can
+only reference it (with a @code{goto} statement, or by taking its
+address) within the block in which it was declared.
A local label declaration looks like this:
-@example
+@smallexample
__label__ @var{label};
-@end example
+@end smallexample
@noindent
or
-@example
+@smallexample
__label__ @var{label1}, @var{label2}, /* @r{@dots{}} */;
-@end example
+@end smallexample
-Local label declarations must come at the beginning of the statement
-expression, right after the @samp{(@{}, before any ordinary
-declarations.
+Local label declarations must come at the beginning of the block,
+before any ordinary declarations or statements.
The label declaration defines the label @emph{name}, but does not define
the label itself. You must do this in the usual way, with
@code{@var{label}:}, within the statements of the statement expression.
-The local label feature is useful because statement expressions are
-often used in macros. If the macro contains nested loops, a @code{goto}
-can be useful for breaking out of them. However, an ordinary label
-whose scope is the whole function cannot be used: if the macro can be
-expanded several times in one function, the label will be multiply
-defined in that function. A local label avoids this problem. For
-example:
+The local label feature is useful for complex macros. If a macro
+contains nested loops, a @code{goto} can be useful for breaking out of
+them. However, an ordinary label whose scope is the whole function
+cannot be used: if the macro can be expanded several times in one
+function, the label will be multiply defined in that function. A
+local label avoids this problem. For example:
-@example
+@smallexample
+#define SEARCH(value, array, target) \
+do @{ \
+ __label__ found; \
+ typeof (target) _SEARCH_target = (target); \
+ typeof (*(array)) *_SEARCH_array = (array); \
+ int i, j; \
+ int value; \
+ for (i = 0; i < max; i++) \
+ for (j = 0; j < max; j++) \
+ if (_SEARCH_array[i][j] == _SEARCH_target) \
+ @{ (value) = i; goto found; @} \
+ (value) = -1; \
+ found:; \
+@} while (0)
+@end smallexample
+
+This could also be written using a statement-expression:
+
+@smallexample
#define SEARCH(array, target) \
(@{ \
__label__ found; \
found: \
value; \
@})
-@end example
+@end smallexample
+
+Local label declarations also make the labels they declare visible to
+nested functions, if there are any. @xref{Nested Functions}, for details.
@node Labels as Values
@section Labels as Values
value has type @code{void *}. This value is a constant and can be used
wherever a constant of that type is valid. For example:
-@example
+@smallexample
void *ptr;
/* @r{@dots{}} */
ptr = &&foo;
-@end example
+@end smallexample
To use these values, you need to be able to jump to one. This is done
with the computed goto statement@footnote{The analogous feature in
C, where one can do more than simply store label addresses in label
variables.}, @code{goto *@var{exp};}. For example,
-@example
+@smallexample
goto *ptr;
-@end example
+@end smallexample
@noindent
Any expression of type @code{void *} is allowed.
One way of using these constants is in initializing a static array that
will serve as a jump table:
-@example
+@smallexample
static void *array[] = @{ &&foo, &&bar, &&hack @};
-@end example
+@end smallexample
Then you can select a label with indexing, like this:
-@example
+@smallexample
goto *array[i];
-@end example
+@end smallexample
@noindent
Note that this does not check whether the subscript is in bounds---array
An alternate way to write the above example is
-@example
+@smallexample
static const int array[] = @{ &&foo - &&foo, &&bar - &&foo,
&&hack - &&foo @};
goto *(&&foo + array[i]);
-@end example
+@end smallexample
@noindent
This is more friendly to code living in shared libraries, as it reduces
name is local to the block where it is defined. For example, here we
define a nested function named @code{square}, and call it twice:
-@example
+@smallexample
@group
foo (double a, double b)
@{
return square (a) + square (b);
@}
@end group
-@end example
+@end smallexample
The nested function can access all the variables of the containing
function that are visible at the point of its definition. This is
called @dfn{lexical scoping}. For example, here we show a nested
function which uses an inherited variable named @code{offset}:
-@example
+@smallexample
@group
bar (int *array, int offset, int size)
@{
/* @r{@dots{}} */ access (array, i) /* @r{@dots{}} */
@}
@end group
-@end example
+@end smallexample
Nested function definitions are permitted within functions in the places
where variable definitions are allowed; that is, in any block, before
It is possible to call the nested function from outside the scope of its
name by storing its address or passing the address to another function:
-@example
+@smallexample
hack (int *array, int size)
@{
void store (int index, int value)
intermediate (store, size);
@}
-@end example
+@end smallexample
Here, the function @code{intermediate} receives the address of
@code{store} as an argument. If @code{intermediate} calls @code{store},
containing function, exiting the nested function which did the
@code{goto} and any intermediate functions as well. Here is an example:
-@example
+@smallexample
@group
bar (int *array, int offset, int size)
@{
return -1;
@}
@end group
-@end example
+@end smallexample
A nested function always has internal linkage. Declaring one with
@code{extern} is erroneous. If you need to declare the nested function
before its definition, use @code{auto} (which is otherwise meaningless
for function declarations).
-@example
+@smallexample
bar (int *array, int offset, int size)
@{
__label__ failure;
@}
/* @r{@dots{}} */
@}
-@end example
+@end smallexample
@node Constructing Calls
@section Constructing Function Calls
the function tried to return (as long as your caller expects
that data type).
+However, these built-in functions may interact badly with some
+sophisticated features or other extensions of the language. It
+is, therefore, not recommended to use them outside very simple
+functions acting as mere forwarders for their arguments.
+
@deftypefn {Built-in Function} {void *} __builtin_apply_args ()
This built-in function returns a pointer to data
describing how to perform a call with the same arguments as were passed
There are two ways of writing the argument to @code{typeof}: with an
expression or with a type. Here is an example with an expression:
-@example
+@smallexample
typeof (x[0](1))
-@end example
+@end smallexample
@noindent
This assumes that @code{x} is an array of pointers to functions;
Here is an example with a typename as the argument:
-@example
+@smallexample
typeof (int *)
-@end example
+@end smallexample
@noindent
Here the type described is that of pointers to @code{int}.
be used to define a safe ``maximum'' macro that operates on any
arithmetic type and evaluates each of its arguments exactly once:
-@example
+@smallexample
#define max(a,b) \
(@{ typeof (a) _a = (a); \
typeof (b) _b = (b); \
_a > _b ? _a : _b; @})
-@end example
+@end smallexample
@cindex underscores in variables in macros
@cindex @samp{_} in variables in macros
@item
This declares @code{y} with the type of what @code{x} points to.
-@example
+@smallexample
typeof (*x) y;
-@end example
+@end smallexample
@item
This declares @code{y} as an array of such values.
-@example
+@smallexample
typeof (*x) y[4];
-@end example
+@end smallexample
@item
This declares @code{y} as an array of pointers to characters:
-@example
+@smallexample
typeof (typeof (char *)[4]) y;
-@end example
+@end smallexample
@noindent
It is equivalent to the following traditional C declaration:
-@example
+@smallexample
char *y[4];
-@end example
+@end smallexample
To see the meaning of the declaration using @code{typeof}, and why it
might be a useful way to write, let's rewrite it with these macros:
-@example
+@smallexample
#define pointer(T) typeof(T *)
#define array(T, N) typeof(T [N])
-@end example
+@end smallexample
@noindent
Now the declaration can be rewritten this way:
-@example
+@smallexample
array (pointer (char), 4) y;
-@end example
+@end smallexample
@noindent
Thus, @code{array (pointer (char), 4)} is the type of arrays of 4
@emph{Compatibility Note:} In addition to @code{typeof}, GCC 2 supported
a more limited extension which permitted one to write
-@example
+@smallexample
typedef @var{T} = @var{expr};
-@end example
+@end smallexample
@noindent
with the effect of declaring @var{T} to have the type of the expression
3.0 and 3.2 will crash; 3.2.1 and later give an error). Code which
relies on it should be rewritten to use @code{typeof}:
-@example
+@smallexample
typedef typeof(@var{expr}) @var{T};
-@end example
+@end smallexample
@noindent
This will work with all versions of GCC@.
-@node Lvalues
-@section Generalized Lvalues
-@cindex compound expressions as lvalues
-@cindex expressions, compound, as lvalues
-@cindex conditional expressions as lvalues
-@cindex expressions, conditional, as lvalues
-@cindex casts as lvalues
-@cindex generalized lvalues
-@cindex lvalues, generalized
-@cindex extensions, @code{?:}
-@cindex @code{?:} extensions
-
-Compound expressions, conditional expressions and casts are allowed as
-lvalues provided their operands are lvalues. This means that you can take
-their addresses or store values into them.
-
-Standard C++ allows compound expressions and conditional expressions as
-lvalues, and permits casts to reference type, so use of this extension
-is deprecated for C++ code.
-
-For example, a compound expression can be assigned, provided the last
-expression in the sequence is an lvalue. These two expressions are
-equivalent:
-
-@example
-(a, b) += 5
-a, (b += 5)
-@end example
-
-Similarly, the address of the compound expression can be taken. These two
-expressions are equivalent:
-
-@example
-&(a, b)
-a, &b
-@end example
-
-A conditional expression is a valid lvalue if its type is not void and the
-true and false branches are both valid lvalues. For example, these two
-expressions are equivalent:
-
-@example
-(a ? b : c) = 5
-(a ? b = 5 : (c = 5))
-@end example
-
-A cast is a valid lvalue if its operand is an lvalue. A simple
-assignment whose left-hand side is a cast works by converting the
-right-hand side first to the specified type, then to the type of the
-inner left-hand side expression. After this is stored, the value is
-converted back to the specified type to become the value of the
-assignment. Thus, if @code{a} has type @code{char *}, the following two
-expressions are equivalent:
-
-@example
-(int)a = 5
-(int)(a = (char *)(int)5)
-@end example
-
-An assignment-with-arithmetic operation such as @samp{+=} applied to a cast
-performs the arithmetic using the type resulting from the cast, and then
-continues as in the previous case. Therefore, these two expressions are
-equivalent:
-
-@example
-(int)a += 5
-(int)(a = (char *)(int) ((int)a + 5))
-@end example
-
-You cannot take the address of an lvalue cast, because the use of its
-address would not work out coherently. Suppose that @code{&(int)f} were
-permitted, where @code{f} has type @code{float}. Then the following
-statement would try to store an integer bit-pattern where a floating
-point number belongs:
-
-@example
-*&(int)f = 1;
-@end example
-
-This is quite different from what @code{(int)f = 1} would do---that
-would convert 1 to floating point and store it. Rather than cause this
-inconsistency, we think it is better to prohibit use of @samp{&} on a cast.
-
-If you really do want an @code{int *} pointer with the address of
-@code{f}, you can simply write @code{(int *)&f}.
-
@node Conditionals
@section Conditionals with Omitted Operands
@cindex conditional expressions, extensions
Therefore, the expression
-@example
+@smallexample
x ? : y
-@end example
+@end smallexample
@noindent
has the value of @code{x} if that is nonzero; otherwise, the value of
This example is perfectly equivalent to
-@example
+@smallexample
x ? x : y
-@end example
+@end smallexample
@cindex side effect in ?:
@cindex ?: side effect
last element of a structure which is really a header for a variable-length
object:
-@example
+@smallexample
struct line @{
int length;
char contents[0];
struct line *thisline = (struct line *)
malloc (sizeof (struct line) + this_length);
thisline->length = this_length;
-@end example
+@end smallexample
In ISO C90, you would have to give @code{contents} a length of 1, which
means either you waste space or complicate the argument to @code{malloc}.
I.e.@: in the following, @code{f1} is constructed as if it were declared
like @code{f2}.
-@example
+@smallexample
struct f1 @{
int x; int y[];
@} f1 = @{ 1, @{ 2, 3, 4 @} @};
struct f2 @{
struct f1 f1; int data[3];
@} f2 = @{ @{ 1 @}, @{ 2, 3, 4 @} @};
-@end example
+@end smallexample
@noindent
The convenience of this extension is that @code{f1} has the desired
non-empty initialization except when the structure is the top-level
object. For example:
-@example
+@smallexample
struct foo @{ int x; int y[]; @};
struct bar @{ struct foo z; @};
struct bar b = @{ @{ 1, @{ 2, 3, 4 @} @} @}; // @r{Invalid.}
struct bar c = @{ @{ 1, @{ @} @} @}; // @r{Valid.}
struct foo d[1] = @{ @{ 1 @{ 2, 3, 4 @} @} @}; // @r{Invalid.}
-@end example
+@end smallexample
+
+@node Empty Structures
+@section Structures With No Members
+@cindex empty structures
+@cindex zero-size structures
+
+GCC permits a C structure to have no members:
+
+@smallexample
+struct empty @{
+@};
+@end smallexample
+
+The structure will have size zero. In C++, empty structures are part
+of the language. G++ treats empty structures as if they had a single
+member of type @code{char}.
@node Variable Length
@section Arrays of Variable Length
declaration and deallocated when the brace-level is exited. For
example:
-@example
+@smallexample
FILE *
concat_fopen (char *s1, char *s2, char *mode)
@{
strcat (str, s2);
return fopen (str, mode);
@}
-@end example
+@end smallexample
@cindex scope of a variable length array
@cindex variable-length array scope
You can also use variable-length arrays as arguments to functions:
-@example
+@smallexample
struct entry
tester (int len, char data[len][len])
@{
/* @r{@dots{}} */
@}
-@end example
+@end smallexample
The length of an array is computed once when the storage is allocated
and is remembered for the scope of the array in case you access it with
If you want to pass the array first and the length afterward, you can
use a forward declaration in the parameter list---another GNU extension.
-@example
+@smallexample
struct entry
tester (int len; char data[len][len], int len)
@{
/* @r{@dots{}} */
@}
-@end example
+@end smallexample
@cindex parameter forward declaration
The @samp{int len} before the semicolon is a @dfn{parameter forward
allowed you to give a name to the variable arguments just like any other
argument. Here is an example:
-@example
+@smallexample
#define debug(format, args...) fprintf (stderr, format, args)
-@end example
+@end smallexample
This is in all ways equivalent to the ISO C example above, but arguably
more readable and descriptive.
this invocation is invalid in ISO C, because there is no comma after
the string:
-@example
+@smallexample
debug ("A message")
-@end example
+@end smallexample
GNU CPP permits you to completely omit the variable arguments in this
way. In the above examples, the compiler would complain, though since
Recently, the preprocessor has relaxed its treatment of escaped
newlines. Previously, the newline had to immediately follow a
-backslash. The current implementation allows whitespace in the form of
-spaces, horizontal and vertical tabs, and form feeds between the
+backslash. The current implementation allows whitespace in the form
+of spaces, horizontal and vertical tabs, and form feeds between the
backslash and the subsequent newline. The preprocessor issues a
warning, but treats it as a valid escaped newline and combines the two
lines to form a single logical line. This works within comments and
-tokens, including multi-line strings, as well as between tokens.
-Comments are @emph{not} treated as whitespace for the purposes of this
-relaxation, since they have not yet been replaced with spaces.
-
-@node Multi-line Strings
-@section String Literals with Embedded Newlines
-@cindex multi-line string literals
-
-As an extension, GNU CPP permits string literals to cross multiple lines
-without escaping the embedded newlines. Each embedded newline is
-replaced with a single @samp{\n} character in the resulting string
-literal, regardless of what form the newline took originally.
-
-CPP currently allows such strings in directives as well (other than the
-@samp{#include} family). This is deprecated and will eventually be
-removed.
+tokens, as well as between tokens. Comments are @emph{not} treated as
+whitespace for the purposes of this relaxation, since they have not
+yet been replaced with spaces.
@node Subscripting
@section Non-Lvalue Arrays May Have Subscripts
pointers outside C99 mode. For example,
this is valid in GNU C though not valid in C89:
-@example
+@smallexample
@group
struct foo @{int a[4];@};
return f().a[index];
@}
@end group
-@end example
+@end smallexample
@node Pointer Arith
@section Arithmetic on @code{void}- and Function-Pointers
automatic variable are not required to be constant expressions in GNU C@.
Here is an example of an initializer with run-time varying elements:
-@example
+@smallexample
foo (float f, float g)
@{
float beat_freqs[2] = @{ f-g, f+g @};
/* @r{@dots{}} */
@}
-@end example
+@end smallexample
@node Compound Literals
@section Compound Literals
Usually, the specified type is a structure. Assume that
@code{struct foo} and @code{structure} are declared as shown:
-@example
+@smallexample
struct foo @{int a; char b[2];@} structure;
-@end example
+@end smallexample
@noindent
Here is an example of constructing a @code{struct foo} with a compound literal:
-@example
+@smallexample
structure = ((struct foo) @{x + y, 'a', 0@});
-@end example
+@end smallexample
@noindent
This is equivalent to writing the following:
-@example
+@smallexample
@{
struct foo temp = @{x + y, 'a', 0@};
structure = temp;
@}
-@end example
+@end smallexample
You can also construct an array. If all the elements of the compound literal
are (made up of) simple constant expressions, suitable for use in
literal can be coerced to a pointer to its first element and used in
such an initializer, as shown here:
-@example
+@smallexample
char **foo = (char *[]) @{ "x", "y", "z" @};
-@end example
+@end smallexample
Compound literals for scalar types and union types are is
also allowed, but then the compound literal is equivalent
If the object being initialized has array type of unknown size, the size is
determined by compound literal size.
-@example
+@smallexample
static struct foo x = (struct foo) @{1, 'a', 'b'@};
static int y[] = (int []) @{1, 2, 3@};
static int z[] = (int [3]) @{1@};
-@end example
+@end smallexample
@noindent
The above lines are equivalent to the following:
-@example
+@smallexample
static struct foo x = @{1, 'a', 'b'@};
static int y[] = @{1, 2, 3@};
static int z[] = @{1, 0, 0@};
-@end example
+@end smallexample
@node Designated Inits
@section Designated Initializers
To specify an array index, write
@samp{[@var{index}] =} before the element value. For example,
-@example
+@smallexample
int a[6] = @{ [4] = 29, [2] = 15 @};
-@end example
+@end smallexample
@noindent
is equivalent to
-@example
+@smallexample
int a[6] = @{ 0, 0, 15, 0, 29, 0 @};
-@end example
+@end smallexample
@noindent
The index values must be constant expressions, even if the array being
@samp{[@var{first} ... @var{last}] = @var{value}}. This is a GNU
extension. For example,
-@example
+@smallexample
int widths[] = @{ [0 ... 9] = 1, [10 ... 99] = 2, [100] = 3 @};
-@end example
+@end smallexample
@noindent
If the value in it has side-effects, the side-effects will happen only once,
with @samp{.@var{fieldname} =} before the element value. For example,
given the following structure,
-@example
+@smallexample
struct point @{ int x, y; @};
-@end example
+@end smallexample
@noindent
the following initialization
-@example
+@smallexample
struct point p = @{ .y = yvalue, .x = xvalue @};
-@end example
+@end smallexample
@noindent
is equivalent to
-@example
+@smallexample
struct point p = @{ xvalue, yvalue @};
-@end example
+@end smallexample
Another syntax which has the same meaning, obsolete since GCC 2.5, is
@samp{@var{fieldname}:}, as shown here:
-@example
+@smallexample
struct point p = @{ y: yvalue, x: xvalue @};
-@end example
+@end smallexample
@cindex designators
The @samp{[@var{index}]} or @samp{.@var{fieldname}} is known as a
syntax) when initializing a union, to specify which element of the union
should be used. For example,
-@example
+@smallexample
union foo @{ int i; double d; @};
union foo f = @{ .d = 4 @};
-@end example
+@end smallexample
@noindent
will convert 4 to a @code{double} to store it in the union using
does not have a designator applies to the next consecutive element of the
array or structure. For example,
-@example
+@smallexample
int a[6] = @{ [1] = v1, v2, [4] = v4 @};
-@end example
+@end smallexample
@noindent
is equivalent to
-@example
+@smallexample
int a[6] = @{ 0, v1, v2, 0, v4, 0 @};
-@end example
+@end smallexample
Labeling the elements of an array initializer is especially useful
when the indices are characters or belong to an @code{enum} type.
For example:
-@example
+@smallexample
int whitespace[256]
= @{ [' '] = 1, ['\t'] = 1, ['\h'] = 1,
['\f'] = 1, ['\n'] = 1, ['\r'] = 1 @};
-@end example
+@end smallexample
@cindex designator lists
You can also write a series of @samp{.@var{fieldname}} and
You can specify a range of consecutive values in a single @code{case} label,
like this:
-@example
+@smallexample
case @var{low} ... @var{high}:
-@end example
+@end smallexample
@noindent
This has the same effect as the proper number of individual @code{case}
This feature is especially useful for ranges of ASCII character codes:
-@example
+@smallexample
case 'A' ... 'Z':
-@end example
+@end smallexample
@strong{Be careful:} Write spaces around the @code{...}, for otherwise
it may be parsed wrong when you use it with integer values. For example,
write this:
-@example
+@smallexample
case 1 ... 5:
-@end example
+@end smallexample
@noindent
rather than this:
-@example
+@smallexample
case 1...5:
-@end example
+@end smallexample
@node Cast to Union
@section Cast to a Union Type
The types that may be cast to the union type are those of the members
of the union. Thus, given the following union and variables:
-@example
+@smallexample
union foo @{ int i; double d; @};
int x;
double y;
-@end example
+@end smallexample
@noindent
both @code{x} and @code{y} can be cast to type @code{union foo}.
Using the cast as the right-hand side of an assignment to a variable of
union type is equivalent to storing in a member of the union:
-@example
+@smallexample
union foo u;
/* @r{@dots{}} */
u = (union foo) x @equiv{} u.i = x
u = (union foo) y @equiv{} u.d = y
-@end example
+@end smallexample
You can also use the union cast as a function argument:
-@example
+@smallexample
void hack (union foo);
/* @r{@dots{}} */
hack ((union foo) x);
-@end example
+@end smallexample
@node Mixed Declarations
@section Mixed Declarations and Code
within compound statements. As an extension, GCC also allows this in
C89 mode. For example, you could do:
-@example
+@smallexample
int i;
/* @r{@dots{}} */
i++;
int j = i + 2;
-@end example
+@end smallexample
Each identifier is visible from where it is declared until the end of
the enclosing block.
@code{format}, @code{format_arg}, @code{no_instrument_function},
@code{section}, @code{constructor}, @code{destructor}, @code{used},
@code{unused}, @code{deprecated}, @code{weak}, @code{malloc},
-@code{alias}, and @code{nonnull}. Several other attributes are defined
-for functions on particular target systems. Other attributes, including
-@code{section} are supported for variables declarations
+@code{alias}, @code{warn_unused_result} and @code{nonnull}. Several other
+attributes are defined for functions on particular target systems. Other
+attributes, including @code{section} are supported for variables declarations
(@pxref{Variable Attributes}) and for types (@pxref{Type Attributes}).
You may also specify attributes with @samp{__} preceding and following
better code. More importantly, it helps avoid spurious warnings of
uninitialized variables.
+The @code{noreturn} keyword does not affect the exceptional path when that
+applies: a @code{noreturn}-marked function may still return to the caller
+by throwing an exception.
+
Do not assume that registers saved by the calling function are
restored before calling the @code{noreturn} function.
@item unused
This attribute, attached to a function, means that the function is meant
to be possibly unused. GCC will not produce a warning for this
-function. GNU C++ does not currently support this attribute as
-definitions without parameters are valid in C++.
+function.
@cindex @code{used} attribute.
@item used
The @code{deprecated} attribute can also be used for variables and
types (@pxref{Variable Attributes}, @pxref{Type Attributes}.)
+@item warn_unused_result
+@cindex @code{warn_unused_result} attribute
+The @code{warn_unused_result} attribute causes a warning to be emitted
+if a caller of the function with this attribute does not use its
+return value. This is useful for functions where not checking
+the result is either a security problem or always a bug, such as
+@code{realloc}.
+
+@smallexample
+int fn () __attribute__ ((warn_unused_result));
+int foo ()
+@{
+ if (fn () < 0) return -1;
+ fn ();
+ return 0;
+@}
+@end smallexample
+
+results in warning on line 5.
+
@item weak
@cindex @code{weak} attribute
The @code{weak} attribute causes the declaration to be emitted as a weak
@item malloc
@cindex @code{malloc} attribute
The @code{malloc} attribute is used to tell the compiler that a function
-may be treated as if it were the malloc function. The compiler assumes
-that calls to malloc result in a pointers that cannot alias anything.
+may be treated as if any non-@code{NULL} pointer it returns cannot
+alias any other pointer valid when the function returns.
This will often improve optimization.
+Standard functions with this property include @code{malloc} and
+@code{calloc}. @code{realloc}-like functions have this property as
+long as the old pointer is never referred to (including comparing it
+to the new pointer) after the function returns a non-@code{NULL}
+value.
@item alias ("@var{target}")
@cindex @code{alias} attribute
int i __attribute__ ((visibility ("hidden")));
@end smallexample
-See the ELF gABI for complete details, but the short story is
+See the ELF gABI for complete details, but the short story is:
@table @dfn
@item default
-Default visibility is the normal case for ELF. This value is
+Default visibility is the normal case for ELF. This value is
available for the visibility attribute to override other options
that may change the assumed visibility of symbols.
Internal visibility is like hidden visibility, but with additional
processor specific semantics. Unless otherwise specified by the psABI,
gcc defines internal visibility to mean that the function is @emph{never}
-called from another module. Note that hidden symbols, while then cannot
+called from another module. Note that hidden symbols, while they cannot
be referenced directly by other modules, can be referenced indirectly via
function pointers. By indicating that a symbol cannot be called from
outside the module, gcc may for instance omit the load of a PIC register
Not all ELF targets support this attribute.
-@item tls_model ("@var{tls_model}")
-@cindex @code{tls_model} attribute
-The @code{tls_model} attribute sets thread-local storage model
-(@pxref{Thread-Local}) of a particular @code{__thread} variable,
-overriding @code{-ftls-model=} command line switch on a per-variable
-basis.
-The @var{tls_model} argument should be one of @code{global-dynamic},
-@code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
-
@item regparm (@var{number})
+@cindex @code{regparm} attribute
@cindex functions that are passed arguments in registers on the 386
On the Intel 386, the @code{regparm} attribute causes the compiler to
pass up to @var{number} integer arguments in registers EAX,
variable number of arguments will continue to be passed all of their
arguments on the stack.
+Beware that on some ELF systems this attribute is unsuitable for
+global functions in shared libraries with lazy binding (which is the
+default). Lazy binding will send the first call via resolving code in
+the loader, which might assume EAX, EDX and ECX can be clobbered, as
+per the standard calling conventions. Solaris 8 is affected by this.
+GNU systems with GLIBC 2.1 or higher, and FreeBSD, are believed to be
+safe since the loaders there save all registers. (Lazy binding can be
+disabled with the linker or the loader if desired, to avoid the
+problem.)
+
@item stdcall
@cindex functions that pop the argument stack on the 386
On the Intel 386, the @code{stdcall} attribute causes the compiler to
@cindex functions that pop the argument stack on the 386
On the Intel 386, the @code{fastcall} attribute causes the compiler to
pass the first two arguments in the registers ECX and EDX. Subsequent
-arguments are passed on the stack. The called function will pop the
+arguments are passed on the stack. The called function will pop the
arguments off the stack. If the number of arguments is variable all
arguments are pushed on the stack.
both the @option{-mlongcall} switch and the @code{#pragma longcall}
setting.
-@xref{RS/6000 and PowerPC Options}, for more information on when long
-calls are and are not necessary.
+@xref{RS/6000 and PowerPC Options}, for more information on whether long
+calls are necessary.
@item long_call/short_call
@cindex indirect calls on ARM
-This attribute allows to specify how to call a particular function on
+This attribute specifies how a particular function is called on
ARM@. Both attributes override the @option{-mlong-calls} (@pxref{ARM Options})
command line switch and @code{#pragma long_calls} settings. The
@code{long_call} attribute causes the compiler to always call the
@item function_vector
@cindex calling functions through the function vector on the H8/300 processors
-Use this attribute on the H8/300 and H8/300H to indicate that the specified
+Use this attribute on the H8/300, H8/300H, and H8S to indicate that the specified
function should be called through the function vector. Calling a
function through the function vector will reduce code size, however;
the function vector has a limited size (maximum 128 entries on the H8/300
-and 64 entries on the H8/300H) and shares space with the interrupt vector.
+and 64 entries on the H8/300H and H8S) and shares space with the interrupt vector.
You must use GAS and GLD from GNU binutils version 2.7 or later for
this attribute to work correctly.
generate function entry and exit sequences suitable for use in an
interrupt handler when this attribute is present.
-Note, interrupt handlers for the H8/300, H8/300H and SH processors can
-be specified via the @code{interrupt_handler} attribute.
+Note, interrupt handlers for the m68k, H8/300, H8/300H, H8S, and SH processors
+can be specified via the @code{interrupt_handler} attribute.
-Note, on the AVR interrupts will be enabled inside the function.
+Note, on the AVR, interrupts will be enabled inside the function.
-Note, for the ARM you can specify the kind of interrupt to be handled by
+Note, for the ARM, you can specify the kind of interrupt to be handled by
adding an optional parameter to the interrupt attribute like this:
@smallexample
Permissible values for this parameter are: IRQ, FIQ, SWI, ABORT and UNDEF@.
@item interrupt_handler
-@cindex interrupt handler functions on the H8/300 and SH processors
-Use this attribute on the H8/300, H8/300H and SH to indicate that the
-specified function is an interrupt handler. The compiler will generate
+@cindex interrupt handler functions on the m68k, H8/300 and SH processors
+Use this attribute on the m68k, H8/300, H8/300H, H8S, and SH to indicate that
+the specified function is an interrupt handler. The compiler will generate
function entry and exit sequences suitable for use in an interrupt
handler when this attribute is present.
@end smallexample
@item trap_exit
-Use this attribute on the SH for an @code{interrupt_handle} to return using
+Use this attribute on the SH for an @code{interrupt_handler} to return using
@code{trapa} instead of @code{rte}. This attribute expects an integer
argument specifying the trap number to be used.
@item eightbit_data
-@cindex eight bit data on the H8/300 and H8/300H
-Use this attribute on the H8/300 and H8/300H to indicate that the specified
+@cindex eight bit data on the H8/300, H8/300H, and H8S
+Use this attribute on the H8/300, H8/300H, and H8S to indicate that the specified
variable should be placed into the eight bit data section.
The compiler will generate more efficient code for certain operations
on data in the eight bit data area. Note the eight bit data area is limited to
this attribute to work correctly.
@item tiny_data
-@cindex tiny data section on the H8/300H
-Use this attribute on the H8/300H to indicate that the specified
+@cindex tiny data section on the H8/300H and H8S
+Use this attribute on the H8/300H and H8S to indicate that the specified
variable should be placed into the tiny data section.
The compiler will generate more efficient code for loads and stores
on data in the tiny data section. Note the tiny data area is limited to
slightly under 32kbytes of data.
+@item saveall
+@cindex save all registers on the H8/300, H8/300H, and H8S
+Use this attribute on the H8/300, H8/300H, and H8S to indicate that
+all registers except the stack pointer should be saved in the prologue
+regardless of whether they are used or not.
+
@item signal
@cindex signal handler functions on the AVR processors
Use this attribute on the AVR to indicate that the specified
-function is an signal handler. The compiler will generate function
-entry and exit sequences suitable for use in an signal handler when this
-attribute is present. Interrupts will be disabled inside function.
+function is a signal handler. The compiler will generate function
+entry and exit sequences suitable for use in a signal handler when this
+attribute is present. Interrupts will be disabled inside the function.
@item naked
@cindex function without a prologue/epilogue code
Use this attribute on the ARM, AVR, C4x and IP2K ports to indicate that the
-specified function do not need prologue/epilogue sequences generated by
+specified function does not need prologue/epilogue sequences generated by
the compiler. It is up to the programmer to provide these sequences.
@item model (@var{model-name})
@cindex function addressability on the M32R/D
-Use this attribute on the M32R/D to set the addressability of an object,
-and the code generated for a function.
-The identifier @var{model-name} is one of @code{small}, @code{medium},
-or @code{large}, representing each of the code models.
+@cindex variable addressability on the IA-64
+
+On the M32R/D, use this attribute to set the addressability of an
+object, and of the code generated for a function. The identifier
+@var{model-name} is one of @code{small}, @code{medium}, or
+@code{large}, representing each of the code models.
Small model objects live in the lower 16MB of memory (so that their
addresses can be loaded with the @code{ld24} instruction), and are
and may not be reachable with the @code{bl} instruction (the compiler will
generate the much slower @code{seth/add3/jl} instruction sequence).
+On IA-64, use this attribute to set the addressability of an object.
+At present, the only supported identifier for @var{model-name} is
+@code{small}, indicating addressability via ``small'' (22-bit)
+addresses (so that their addresses can be loaded with the @code{addl}
+instruction). Caveat: such addressing is by definition not position
+independent and hence this attribute must not be used for objects
+defined by shared libraries.
+
+@item far
+@cindex functions which handle memory bank switching
+On 68HC11 and 68HC12 the @code{far} attribute causes the compiler to
+use a calling convention that takes care of switching memory banks when
+entering and leaving a function. This calling convention is also the
+default when using the @option{-mlong-calls} option.
+
+On 68HC12 the compiler will use the @code{call} and @code{rtc} instructions
+to call and return from a function.
+
+On 68HC11 the compiler will generate a sequence of instructions
+to invoke a board-specific routine to switch the memory bank and call the
+real function. The board-specific routine simulates a @code{call}.
+At the end of a function, it will jump to a board-specific routine
+instead of using @code{rts}. The board-specific return routine simulates
+the @code{rtc}.
+
+@item near
+@cindex functions which do not handle memory bank switching on 68HC11/68HC12
+On 68HC11 and 68HC12 the @code{near} attribute causes the compiler to
+use the normal calling convention based on @code{jsr} and @code{rts}.
+This attribute can be used to cancel the effect of the @option{-mlong-calls}
+option.
+
+@item dllimport
+@cindex @code{__declspec(dllimport)}
+On Microsoft Windows targets, the @code{dllimport} attribute causes the compiler
+to reference a function or variable via a global pointer to a pointer
+that is set up by the Microsoft Windows dll library. The pointer name is formed by
+combining @code{_imp__} and the function or variable name. The attribute
+implies @code{extern} storage.
+
+Currently, the attribute is ignored for inlined functions. If the
+attribute is applied to a symbol @emph{definition}, an error is reported.
+If a symbol previously declared @code{dllimport} is later defined, the
+attribute is ignored in subsequent references, and a warning is emitted.
+The attribute is also overridden by a subsequent declaration as
+@code{dllexport}.
+
+When applied to C++ classes, the attribute marks non-inlined
+member functions and static data members as imports. However, the
+attribute is ignored for virtual methods to allow creation of vtables
+using thunks.
+
+On cygwin, mingw and arm-pe targets, @code{__declspec(dllimport)} is
+recognized as a synonym for @code{__attribute__ ((dllimport))} for
+compatibility with other Microsoft Windows compilers.
+
+The use of the @code{dllimport} attribute on functions is not necessary,
+but provides a small performance benefit by eliminating a thunk in the
+dll. The use of the @code{dllimport} attribute on imported variables was
+required on older versions of GNU ld, but can now be avoided by passing
+the @option{--enable-auto-import} switch to ld. As with functions, using
+the attribute for a variable eliminates a thunk in the dll.
+
+One drawback to using this attribute is that a pointer to a function or
+variable marked as dllimport cannot be used as a constant address. The
+attribute can be disabled for functions by setting the
+@option{-mnop-fun-dllimport} flag.
+
+@item dllexport
+@cindex @code{__declspec(dllexport)}
+On Microsoft Windows targets the @code{dllexport} attribute causes the compiler to
+provide a global pointer to a pointer in a dll, so that it can be
+referenced with the @code{dllimport} attribute. The pointer name is
+formed by combining @code{_imp__} and the function or variable name.
+
+Currently, the @code{dllexport}attribute is ignored for inlined
+functions, but export can be forced by using the
+@option{-fkeep-inline-functions} flag. The attribute is also ignored for
+undefined symbols.
+
+When applied to C++ classes. the attribute marks defined non-inlined
+member functions and static data members as exports. Static consts
+initialized in-class are not marked unless they are also defined
+out-of-class.
+
+On cygwin, mingw and arm-pe targets, @code{__declspec(dllexport)} is
+recognized as a synonym for @code{__attribute__ ((dllexport))} for
+compatibility with other Microsoft Windows compilers.
+
+Alternative methods for including the symbol in the dll's export table
+are to use a .def file with an @code{EXPORTS} section or, with GNU ld,
+using the @option{--export-all} linker flag.
+
@end table
You can specify multiple attributes in a declaration by separating them
attachment of attributes to their corresponding declarations, whereas
@code{#pragma GCC} is of use for constructs that do not naturally form
part of the grammar. @xref{Other Directives,,Miscellaneous
-Preprocessing Directives, cpp, The C Preprocessor}.
+Preprocessing Directives, cpp, The GNU C Preprocessor}.
@node Attribute Syntax
@section Attribute Syntax
An @dfn{attribute specifier list} is a sequence of one or more attribute
specifiers, not separated by any other tokens.
-An attribute specifier list may appear after the colon following a
+In GNU C, an attribute specifier list may appear after the colon following a
label, other than a @code{case} or @code{default} label. The only
attribute it makes sense to use after a label is @code{unused}. This
feature is intended for code generated by programs which contains labels
that may be unused but which is compiled with @option{-Wall}. It would
not normally be appropriate to use in it human-written code, though it
could be useful in cases where the code that jumps to the label is
-contained within an @code{#ifdef} conditional.
+contained within an @code{#ifdef} conditional. GNU C++ does not permit
+such placement of attribute lists, as it is permissible for a
+declaration, which could begin with an attribute list, to be labelled in
+C++. Declarations cannot be labelled in C90 or C99, so the ambiguity
+does not arise there.
An attribute specifier list may appear as part of a @code{struct},
@code{union} or @code{enum} specifier. It may go either immediately
GNU C extends ISO C to allow a function prototype to override a later
old-style non-prototype definition. Consider the following example:
-@example
+@smallexample
/* @r{Use prototypes unless the compiler is old-fashioned.} */
#ifdef __STDC__
#define P(x) x
@{
return x == 0;
@}
-@end example
+@end smallexample
Suppose the type @code{uid_t} happens to be @code{short}. ISO C does
not allow this example, because subword arguments in old-style
latter type before promotion. Thus in GNU C the above example is
equivalent to the following:
-@example
+@smallexample
int isroot (uid_t);
int
@{
return x == 0;
@}
-@end example
+@end smallexample
@noindent
GNU C++ does not support old-style function definitions, so this
designs, @code{__alignof__ (double)} is 4 or even 2.
Some machines never actually require alignment; they allow reference to any
-data type even at an odd addresses. For these machines, @code{__alignof__}
+data type even at an odd address. For these machines, @code{__alignof__}
reports the @emph{recommended} alignment of a type.
If the operand of @code{__alignof__} is an lvalue rather than a type,
extension (@pxref{Variable Attributes}). For example, after this
declaration:
-@example
+@smallexample
struct foo @{ int x; char y; @} foo1;
-@end example
+@end smallexample
@noindent
the value of @code{__alignof__ (foo1.y)} is 1, even though its actual
The keyword @code{__attribute__} allows you to specify special
attributes of variables or structure fields. This keyword is followed
-by an attribute specification inside double parentheses. Ten
-attributes are currently defined for variables: @code{aligned},
-@code{mode}, @code{nocommon}, @code{packed}, @code{section},
-@code{transparent_union}, @code{unused}, @code{deprecated},
-@code{vector_size}, and @code{weak}. Some other attributes are defined
-for variables on particular target systems. Other attributes are
-available for functions (@pxref{Function Attributes}) and for types
-(@pxref{Type Attributes}). Other front ends might define more
-attributes (@pxref{C++ Extensions,,Extensions to the C++ Language}).
+by an attribute specification inside double parentheses. Some
+attributes are currently defined generically for variables.
+Other attributes are defined for variables on particular target
+systems. Other attributes are available for functions
+(@pxref{Function Attributes}) and for types (@pxref{Type Attributes}).
+Other front ends might define more attributes
+(@pxref{C++ Extensions,,Extensions to the C++ Language}).
You may also specify attributes with @samp{__} preceding and following
each keyword. This allows you to use them in header files without
in an @code{__attribute__} will still only provide you with 8 byte
alignment. See your linker documentation for further information.
+@item cleanup (@var{cleanup_function})
+@cindex @code{cleanup} attribute
+The @code{cleanup} attribute runs a function when the variable goes
+out of scope. This attribute can only be applied to auto function
+scope variables; it may not be applied to parameters or variables
+with static storage duration. The function must take one parameter,
+a pointer to a type compatible with the variable. The return value
+of the function (if any) is ignored.
+
+If @option{-fexceptions} is enabled, then @var{cleanup_function}
+will be run during the stack unwinding that happens during the
+processing of the exception. Note that the @code{cleanup} attribute
+does not allow the exception to be caught, only to perform an action.
+It is undefined what happens if @var{cleanup_function} does not
+return normally.
+
+@item common
+@itemx nocommon
+@cindex @code{common} attribute
+@cindex @code{nocommon} attribute
+@opindex fcommon
+@opindex fno-common
+The @code{common} attribute requests GCC to place a variable in
+``common'' storage. The @code{nocommon} attribute requests the
+opposite -- to allocate space for it directly.
+
+These attributes override the default chosen by the
+@option{-fno-common} and @option{-fcommon} flags respectively.
+
+@item deprecated
+@cindex @code{deprecated} attribute
+The @code{deprecated} attribute results in a warning if the variable
+is used anywhere in the source file. This is useful when identifying
+variables that are expected to be removed in a future version of a
+program. The warning also includes the location of the declaration
+of the deprecated variable, to enable users to easily find further
+information about why the variable is deprecated, or what they should
+do instead. Note that the warning only occurs for uses:
+
+@smallexample
+extern int old_var __attribute__ ((deprecated));
+extern int old_var;
+int new_fn () @{ return old_var; @}
+@end smallexample
+
+results in a warning on line 3 but not line 2.
+
+The @code{deprecated} attribute can also be used for functions and
+types (@pxref{Function Attributes}, @pxref{Type Attributes}.)
+
@item mode (@var{mode})
@cindex @code{mode} attribute
This attribute specifies the data type for the declaration---whichever
@samp{__word__} for the mode of a one-word integer, and @samp{pointer}
or @samp{__pointer__} for the mode used to represent pointers.
-@item nocommon
-@cindex @code{nocommon} attribute
-@opindex fno-common
-This attribute specifies requests GCC not to place a variable
-``common'' but instead to allocate space for it directly. If you
-specify the @option{-fno-common} flag, GCC will do this for all
-variables.
-
-Specifying the @code{nocommon} attribute for a variable provides an
-initialization of zeros. A variable may only be initialized in one
-source file.
-
@item packed
@cindex @code{packed} attribute
The @code{packed} attribute specifies that a variable or structure field
Here is a structure in which the field @code{x} is packed, so that it
immediately follows @code{a}:
-@example
+@smallexample
struct foo
@{
char a;
int x[2] __attribute__ ((packed));
@};
-@end example
+@end smallexample
@item section ("@var{section-name}")
@cindex @code{section} variable attribute
@item shared
@cindex @code{shared} variable attribute
-On Windows NT, in addition to putting variable definitions in a named
+On Microsoft Windows, in addition to putting variable definitions in a named
section, the section can also be shared among all running copies of an
executable or DLL@. For example, this small program defines shared data
by putting it in a named section @code{shared} and marking the section
attribute with a fully initialized global definition because of the way
linkers work. See @code{section} attribute for more information.
-The @code{shared} attribute is only available on Windows NT@.
+The @code{shared} attribute is only available on Microsoft Windows@.
+
+@item tls_model ("@var{tls_model}")
+@cindex @code{tls_model} attribute
+The @code{tls_model} attribute sets thread-local storage model
+(@pxref{Thread-Local}) of a particular @code{__thread} variable,
+overriding @code{-ftls-model=} command line switch on a per-variable
+basis.
+The @var{tls_model} argument should be one of @code{global-dynamic},
+@code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
+
+Not all targets support this attribute.
@item transparent_union
This attribute, attached to a function parameter which is a union, means
to be possibly unused. GCC will not produce a warning for this
variable.
-@item deprecated
-The @code{deprecated} attribute results in a warning if the variable
-is used anywhere in the source file. This is useful when identifying
-variables that are expected to be removed in a future version of a
-program. The warning also includes the location of the declaration
-of the deprecated variable, to enable users to easily find further
-information about why the variable is deprecated, or what they should
-do instead. Note that the warnings only occurs for uses:
-
-@smallexample
-extern int old_var __attribute__ ((deprecated));
-extern int old_var;
-int new_fn () @{ return old_var; @}
-@end smallexample
-
-results in a warning on line 3 but not line 2.
-
-The @code{deprecated} attribute can also be used for functions and
-types (@pxref{Function Attributes}, @pxref{Type Attributes}.)
-
@item vector_size (@var{bytes})
This attribute specifies the vector size for the variable, measured in
bytes. For example, the declaration:
@item weak
The @code{weak} attribute is described in @xref{Function Attributes}.
+@item dllimport
+The @code{dllimport} attribute is described in @xref{Function Attributes}.
+
+@item dlexport
+The @code{dllexport} attribute is described in @xref{Function Attributes}.
+
+@end table
+
+@subsection M32R/D Variable Attributes
+
+One attribute is currently defined for the M32R/D.
+
+@table @code
@item model (@var{model-name})
@cindex variable addressability on the M32R/D
Use this attribute on the M32R/D to set the addressability of an object.
Medium and large model objects may live anywhere in the 32-bit address space
(the compiler will generate @code{seth/add3} instructions to load their
addresses).
+@end table
@subsection i386 Variable Attributes
Two attributes are currently defined for i386 configurations:
@code{ms_struct} and @code{gcc_struct}
+@table @code
@item ms_struct
@itemx gcc_struct
-@cindex @code{ms_struct}
-@cindex @code{gcc_struct}
+@cindex @code{ms_struct} attribute
+@cindex @code{gcc_struct} attribute
If @code{packed} is used on a structure, or if bit-fields are used
it may be that the Microsoft ABI packs them differently
(either via function call or as data in a file), it may be necessary to access
either format.
-Currently @option{-m[no-]ms-bitfields} is provided for the Windows X86
+Currently @option{-m[no-]ms-bitfields} is provided for the Microsoft Windows X86
compilers to match the native Microsoft compiler.
-
@end table
-To specify multiple attributes, separate them by commas within the
-double parentheses: for example, @samp{__attribute__ ((aligned (16),
-packed))}.
-
@node Type Attributes
@section Specifying Attributes of Types
@cindex attribute of types
alignment. See your linker documentation for further information.
@item packed
-This attribute, attached to an @code{enum}, @code{struct}, or
-@code{union} type definition, specified that the minimum required memory
-be used to represent the type.
+This attribute, attached to @code{struct} or @code{union} type
+definition, specifies that each member of the structure or union is
+placed to minimize the memory required. When attached to an @code{enum}
+definition, it indicates that the smallest integral type should be used.
@opindex fshort-enums
Specifying this attribute for @code{struct} and @code{union} types is
flag on the line is equivalent to specifying the @code{packed}
attribute on all @code{enum} definitions.
-You may only specify this attribute after a closing curly brace on an
-@code{enum} definition, not in a @code{typedef} declaration, unless that
-declaration also contains the definition of the @code{enum}.
+In the following example @code{struct my_packed_struct}'s members are
+packed closely together, but the internal layout of its @code{s} member
+is not packed -- to do that, @code{struct my_unpacked_struct} would need to
+be packed too.
+
+@smallexample
+struct my_unpacked_struct
+ @{
+ char c;
+ int i;
+ @};
+
+struct my_packed_struct __attribute__ ((__packed__))
+ @{
+ char c;
+ int i;
+ struct my_unpacked_struct s;
+ @};
+@end smallexample
+
+You may only specify this attribute on the definition of a @code{enum},
+@code{struct} or @code{union}, not on a @code{typedef} which does not
+also define the enumerated type, structure or union.
@item transparent_union
This attribute, attached to a @code{union} type definition, indicates
conversions.
Second, the argument is passed to the function using the calling
-conventions of first member of the transparent union, not the calling
+conventions of the first member of the transparent union, not the calling
conventions of the union itself. All members of the union must have the
same machine representation; this is necessary for this argument passing
to work properly.
arguments to be passed, using the @code{int *} calling convention.
The program can call @code{wait} with arguments of either type:
-@example
+@smallexample
int w1 () @{ int w; return wait (&w); @}
int w2 () @{ union wait w; return wait (&w); @}
-@end example
+@end smallexample
With this interface, @code{wait}'s implementation might look like this:
-@example
+@smallexample
pid_t wait (wait_status_ptr_t p)
@{
return waitpid (-1, p.__ip, 0);
@}
-@end example
+@end smallexample
@item unused
When attached to a type (including a @code{union} or a @code{struct}),
(either via function call or as data in a file), it may be necessary to access
either format.
-Currently @option{-m[no-]ms-bitfields} is provided for the Windows X86
+Currently @option{-m[no-]ms-bitfields} is provided for the Microsoft Windows X86
compilers to match the native Microsoft compiler.
@end table
To declare a function inline, use the @code{inline} keyword in its
declaration, like this:
-@example
+@smallexample
inline int
inc (int *a)
@{
(*a)++;
@}
-@end example
+@end smallexample
(If you are writing a header file to be included in ISO C programs, write
@code{__inline__} instead of @code{inline}. @xref{Alternate Keywords}.)
to be inlined. If any uses of the function remain, they will refer to
the single copy in the library.
-For future compatibility with when GCC implements ISO C99 semantics for
-inline functions, it is best to use @code{static inline} only. (The
+Since GCC eventually will implement ISO C99 semantics for
+inline functions, it is best to use @code{static inline} only
+to guarantee compatibility. (The
existing semantics will remain available when @option{-std=gnu89} is
specified, but eventually the default will be @option{-std=gnu99} and
that will implement the C99 semantics, though it does not do so yet.)
GCC does not inline any functions when not optimizing unless you specify
the @samp{always_inline} attribute for the function, like this:
-@example
+@smallexample
/* Prototype. */
inline void foo (const char) __attribute__((always_inline));
-@end example
+@end smallexample
@node Extended Asm
@section Assembler Instructions with C Expression Operands
For example, here is how to use the 68881's @code{fsinx} instruction:
-@example
+@smallexample
asm ("fsinx %1,%0" : "=f" (result) : "f" (angle));
-@end example
+@end smallexample
@noindent
Here @code{angle} is the C expression for the input operand while
followed by the operand number. Using named operands the above example
could look like:
-@example
+@smallexample
asm ("fsinx %[angle],%[output]"
: [output] "=f" (result)
: [angle] "f" (angle));
-@end example
+@end smallexample
@noindent
Note that the symbolic operand names have no relation whatsoever to
other C identifiers. You may use any name you like, even those of
-existing C symbols, but must ensure that no two operands within the same
+existing C symbols, but you must ensure that no two operands within the same
assembler construct use the same symbolic name.
Output operand expressions must be lvalues; the compiler can check this.
the values in these operands before the instruction are dead and need
not be generated. Extended asm supports input-output or read-write
operands. Use the constraint character @samp{+} to indicate such an
-operand and list it with the output operands.
-
-When the constraints for the read-write operand (or the operand in which
-only some of the bits are to be changed) allows a register, you may, as
-an alternative, logically split its function into two separate operands,
-one input operand and one write-only output operand. The connection
-between them is expressed by constraints which say they need to be in
-the same location when the instruction executes. You can use the same C
-expression for both operands, or different expressions. For example,
-here we write the (fictitious) @samp{combine} instruction with
-@code{bar} as its read-only source operand and @code{foo} as its
-read-write destination:
+operand and list it with the output operands. You should only use
+read-write operands when the constraints for the operand (or the
+operand in which only some of the bits are to be changed) allow a
+register.
+
+You may, as an alternative, logically split its function into two
+separate operands, one input operand and one write-only output
+operand. The connection between them is expressed by constraints
+which say they need to be in the same location when the instruction
+executes. You can use the same C expression for both operands, or
+different expressions. For example, here we write the (fictitious)
+@samp{combine} instruction with @code{bar} as its read-only source
+operand and @code{foo} as its read-write destination:
-@example
+@smallexample
asm ("combine %2,%0" : "=r" (foo) : "0" (foo), "g" (bar));
-@end example
+@end smallexample
@noindent
The constraint @samp{"0"} for operand 1 says that it must occupy the
same place in the generated assembler code. The following would not
work reliably:
-@example
+@smallexample
asm ("combine %2,%0" : "=r" (foo) : "r" (foo), "g" (bar));
-@end example
+@end smallexample
Various optimizations or reloading could cause operands 0 and 1 to be in
different registers; GCC knows no reason not to do so. For example, the
As of GCC version 3.1, one may write @code{[@var{name}]} instead of
the operand number for a matching constraint. For example:
-@example
+@smallexample
asm ("cmoveq %1,%2,%[result]"
: [result] "=r"(result)
: "r" (test), "r"(new), "[result]"(old));
-@end example
+@end smallexample
Some instructions clobber specific hard registers. To describe this,
write a third colon after the input operands, followed by the names of
the clobbered hard registers (given as strings). Here is a realistic
example for the VAX:
-@example
+@smallexample
asm volatile ("movc3 %0,%1,%2"
: /* no outputs */
: "g" (from), "g" (to), "g" (count)
: "r0", "r1", "r2", "r3", "r4", "r5");
-@end example
+@end smallexample
You may not write a clobber description in a way that overlaps with an
input or output operand. For example, you may not have an operand
condition code is handled differently, and specifying @samp{cc} has no
effect. But it is valid no matter what the machine.
-If your assembler instruction modifies memory in an unpredictable
+If your assembler instructions access memory in an unpredictable
fashion, add @samp{memory} to the list of clobbered registers. This
-will cause GCC to not keep memory values cached in registers across
-the assembler instruction. You will also want to add the
-@code{volatile} keyword if the memory affected is not listed in the
-inputs or outputs of the @code{asm}, as the @samp{memory} clobber does
-not count as a side-effect of the @code{asm}.
+will cause GCC to not keep memory values cached in registers across the
+assembler instruction and not optimize stores or loads to that memory.
+You will also want to add the @code{volatile} keyword if the memory
+affected is not listed in the inputs or outputs of the @code{asm}, as
+the @samp{memory} clobber does not count as a side-effect of the
+@code{asm}. If you know how large the accessed memory is, you can add
+it as input or output but if this is not known, you should add
+@samp{memory}. As an example, if you access ten bytes of a string, you
+can use a memory input like:
+
+@example
+@{"m"( (@{ struct @{ char x[10]; @} *p = (void *)ptr ; *p; @}) )@}.
+@end example
+
+Note that in the following example the memory input is necessary,
+otherwise GCC might optimize the store to @code{x} away:
+@example
+int foo ()
+@{
+ int x = 42;
+ int *y = &x;
+ int result;
+ asm ("magic stuff accessing an 'int' pointed to by '%1'"
+ "=&d" (r) : "a" (y), "m" (*y));
+ return result;
+@}
+@end example
You can put multiple assembler instructions together in a single
@code{asm} template, separated by the characters normally used in assembly
is an example of multiple instructions in a template; it assumes the
subroutine @code{_foo} accepts arguments in registers 9 and 10:
-@example
+@smallexample
asm ("movl %0,r9\n\tmovl %1,r10\n\tcall _foo"
: /* no outputs */
: "g" (from), "g" (to)
: "r9", "r10");
-@end example
+@end smallexample
Unless an output operand has the @samp{&} constraint modifier, GCC
may allocate it in the same register as an unrelated input operand, on
instruction, you must include a branch and a label in the @code{asm}
construct, as follows:
-@example
+@smallexample
asm ("clr %0\n\tfrob %1\n\tbeq 0f\n\tmov #1,%0\n0:"
: "g" (result)
: "g" (input));
-@end example
+@end smallexample
@noindent
This assumes your assembler supports local labels, as the GNU assembler
Usually the most convenient way to use these @code{asm} instructions is to
encapsulate them in macros that look like functions. For example,
-@example
+@smallexample
#define sin(x) \
(@{ double __value, __arg = (x); \
asm ("fsinx %1,%0": "=f" (__value): "f" (__arg)); \
__value; @})
-@end example
+@end smallexample
@noindent
Here the variable @code{__arg} is used to make sure that the instruction
significantly, or combined, by writing the keyword @code{volatile} after
the @code{asm}. For example:
-@example
+@smallexample
#define get_and_set_priority(new) \
(@{ int __old; \
asm volatile ("get_and_set_priority %0, %1" \
: "=g" (__old) : "g" (new)); \
__old; @})
-@end example
+@end smallexample
@noindent
If you write an @code{asm} instruction with no outputs, GCC will know
instruction.) In addition, GCC will not reschedule instructions
across a volatile @code{asm} instruction. For example:
-@example
+@smallexample
*(volatile int *)addr = foo;
asm volatile ("eieio" : : );
-@end example
+@end smallexample
@noindent
Assume @code{addr} contains the address of a memory mapped device
programs, write @code{__asm__} instead of @code{asm}. @xref{Alternate
Keywords}.
+@subsection Size of an @code{asm}
+
+Some targets require that GCC track the size of each instruction used in
+order to generate correct code. Because the final length of an
+@code{asm} is only known by the assembler, GCC must make an estimate as
+to how big it will be. The estimate is formed by counting the number of
+statements in the pattern of the @code{asm} and multiplying that by the
+length of the longest instruction on that processor. Statements in the
+@code{asm} are identified by newline characters and whatever statement
+separator characters are supported by the assembler; on most processors
+this is the `@code{;}' character.
+
+Normally, GCC's estimate is perfectly adequate to ensure that correct
+code is generated, but it is possible to confuse the compiler if you use
+pseudo instructions or assembler macros that expand into multiple real
+instructions or if you use assembler directives that expand to more
+space in the object file than would be needed for a single instruction.
+If this happens then the assembler will produce a diagnostic saying that
+a label is unreachable.
+
@subsection i386 floating point asm operands
There are several rules on the usage of stack-like regs in
It is possible that if an input dies in an insn, reload might
use the input reg for an output reload. Consider this example:
-@example
+@smallexample
asm ("foo" : "=t" (a) : "f" (b));
-@end example
+@end smallexample
This asm says that input B is not popped by the asm, and that
the asm pushes a result onto the reg-stack, i.e., the stack is one
The asm above would be written as
-@example
+@smallexample
asm ("foo" : "=&t" (a) : "f" (b));
-@end example
+@end smallexample
@item
Some operands need to be in particular places on the stack. All
Here are a couple of reasonable asms to want to write. This asm
takes one input, which is internally popped, and produces two outputs.
-@example
+@smallexample
asm ("fsincos" : "=t" (cos), "=u" (sin) : "0" (inp));
-@end example
+@end smallexample
This asm takes two inputs, which are popped by the @code{fyl2xp1} opcode,
and replaces them with one output. The user must code the @code{st(1)}
clobber for reg-stack.c to know that @code{fyl2xp1} pops both inputs.
-@example
+@smallexample
asm ("fyl2xp1" : "=t" (result) : "0" (x), "u" (y) : "st(1)");
-@end example
+@end smallexample
@include md.texi
function or variable by writing the @code{asm} (or @code{__asm__})
keyword after the declarator as follows:
-@example
+@smallexample
int foo asm ("myfoo") = 2;
-@end example
+@end smallexample
@noindent
This specifies that the name to be used for the variable @code{foo} in
you can get the same effect by writing a declaration for the function
before its definition and putting @code{asm} there, like this:
-@example
+@smallexample
extern func () asm ("FUNC");
func (x, y)
int x, y;
/* @r{@dots{}} */
-@end example
+@end smallexample
It is up to you to make sure that the assembler names you choose do not
conflict with any other assembler symbols. Also, you must not use a
You can define a global register variable in GNU C like this:
-@example
+@smallexample
register int *foo asm ("a5");
-@end example
+@end smallexample
@noindent
Here @code{a5} is the name of the register which should be used. Choose a
You can define a local register variable with a specified register
like this:
-@example
+@smallexample
register int *foo asm ("a5");
-@end example
+@end smallexample
@noindent
Here @code{a5} is the name of the register which should be used. Note
compile with another compiler, you can define the alternate keywords as
macros to replace them with the customary keywords. It looks like this:
-@example
+@smallexample
#ifndef __GNUC__
#define __asm__ asm
#endif
-@end example
+@end smallexample
@findex __extension__
@opindex pedantic
@node Function Names
@section Function Names as Strings
+@cindex @code{__func__} identifier
@cindex @code{__FUNCTION__} identifier
@cindex @code{__PRETTY_FUNCTION__} identifier
-@cindex @code{__func__} identifier
-GCC predefines two magic identifiers to hold the name of the current
-function. The identifier @code{__FUNCTION__} holds the name of the function
-as it appears in the source. The identifier @code{__PRETTY_FUNCTION__}
-holds the name of the function pretty printed in a language specific
-fashion.
+GCC provides three magic variables which hold the name of the current
+function, as a string. The first of these is @code{__func__}, which
+is part of the C99 standard:
+
+@display
+The identifier @code{__func__} is implicitly declared by the translator
+as if, immediately following the opening brace of each function
+definition, the declaration
+
+@smallexample
+static const char __func__[] = "function-name";
+@end smallexample
+
+appeared, where function-name is the name of the lexically-enclosing
+function. This name is the unadorned name of the function.
+@end display
+
+@code{__FUNCTION__} is another name for @code{__func__}. Older
+versions of GCC recognize only this name. However, it is not
+standardized. For maximum portability, we recommend you use
+@code{__func__}, but provide a fallback definition with the
+preprocessor:
+
+@smallexample
+#if __STDC_VERSION__ < 199901L
+# if __GNUC__ >= 2
+# define __func__ __FUNCTION__
+# else
+# define __func__ "<unknown>"
+# endif
+#endif
+@end smallexample
-These names are always the same in a C function, but in a C++ function
-they may be different. For example, this program:
+In C, @code{__PRETTY_FUNCTION__} is yet another name for
+@code{__func__}. However, in C++, @code{__PRETTY_FUNCTION__} contains
+the type signature of the function as well as its bare name. For
+example, this program:
@smallexample
extern "C" @{
@smallexample
__FUNCTION__ = sub
-__PRETTY_FUNCTION__ = int a::sub (int)
-@end smallexample
-
-The compiler automagically replaces the identifiers with a string
-literal containing the appropriate name. Thus, they are neither
-preprocessor macros, like @code{__FILE__} and @code{__LINE__}, nor
-variables. This means that they catenate with other string literals, and
-that they can be used to initialize char arrays. For example
-
-@smallexample
-char here[] = "Function " __FUNCTION__ " in " __FILE__;
-@end smallexample
-
-On the other hand, @samp{#ifdef __FUNCTION__} does not have any special
-meaning inside a function, since the preprocessor does not do anything
-special with the identifier @code{__FUNCTION__}.
-
-Note that these semantics are deprecated, and that GCC 3.2 will handle
-@code{__FUNCTION__} and @code{__PRETTY_FUNCTION__} the same way as
-@code{__func__}. @code{__func__} is defined by the ISO standard C99:
-
-@display
-The identifier @code{__func__} is implicitly declared by the translator
-as if, immediately following the opening brace of each function
-definition, the declaration
-
-@smallexample
-static const char __func__[] = "function-name";
+__PRETTY_FUNCTION__ = void a::sub(int)
@end smallexample
-appeared, where function-name is the name of the lexically-enclosing
-function. This name is the unadorned name of the function.
-@end display
-
-By this definition, @code{__func__} is a variable, not a string literal.
-In particular, @code{__func__} does not catenate with other string
-literals.
-
-In @code{C++}, @code{__FUNCTION__} and @code{__PRETTY_FUNCTION__} are
-variables, declared in the same way as @code{__func__}.
+These identifiers are not preprocessor macros. In GCC 3.3 and
+earlier, in C only, @code{__FUNCTION__} and @code{__PRETTY_FUNCTION__}
+were treated as string literals; they could be used to initialize
+@code{char} arrays, and they could be concatenated with other string
+literals. GCC 3.4 and later treat them as variables, like
+@code{__func__}. In C++, @code{__FUNCTION__} and
+@code{__PRETTY_FUNCTION__} have always been variables.
@node Return Address
@section Getting the Return or Frame Address of a Function
The first step in using these extensions is to provide the necessary data
types. This should be done using an appropriate @code{typedef}:
-@example
+@smallexample
typedef int v4si __attribute__ ((mode(V4SI)));
-@end example
+@end smallexample
The base type @code{int} is effectively ignored by the compiler, the
actual properties of the new type @code{v4si} are defined by the
produce code that uses 4 @code{SIs}.
The types defined in this manner can be used with a subset of normal C
-operations. Currently, gcc will allow using the following operators on
-these types: @code{+, -, *, /, unary minus}@.
+operations. Currently, gcc will allow using the following operators
+on these types: @code{+, -, *, /, unary minus, ^, |, &, ~}@.
The operations behave like C++ @code{valarrays}. Addition is defined as
the addition of the corresponding elements of the operands. For
added to the corresponding 4 elements in @var{b} and the resulting
vector will be stored in @var{c}.
-@example
+@smallexample
typedef int v4si __attribute__ ((mode(V4SI)));
v4si a, b, c;
c = a + b;
-@end example
+@end smallexample
-Subtraction, multiplication, and division operate in a similar manner.
-Likewise, the result of using the unary minus operator on a vector type
-is a vector whose elements are the negative value of the corresponding
+Subtraction, multiplication, division, and the logical operations
+operate in a similar manner. Likewise, the result of using the unary
+minus or complement operators on a vector type is a vector whose
+elements are the negative or complemented values of the corresponding
elements in the operand.
You can declare variables and use them in function calls and returns, as
example, a function to add two vectors and multiply the result by a
third could look like this:
-@example
+@smallexample
v4si f (v4si a, v4si b, v4si c)
@{
v4si tmp = __builtin_addv4si (a, b);
return __builtin_mulv4si (tmp, c);
@}
-@end example
+@end smallexample
@node Other Builtins
@section Other built-in functions provided by GCC
@findex __builtin_islessequal
@findex __builtin_islessgreater
@findex __builtin_isunordered
+@findex _Exit
+@findex _exit
@findex abort
@findex abs
+@findex acos
+@findex acosf
+@findex acosh
+@findex acoshf
+@findex acoshl
+@findex acosl
@findex alloca
+@findex asin
+@findex asinf
+@findex asinh
+@findex asinhf
+@findex asinhl
+@findex asinl
+@findex atan
@findex atan2
@findex atan2f
@findex atan2l
+@findex atanf
+@findex atanh
+@findex atanhf
+@findex atanhl
+@findex atanl
@findex bcmp
@findex bzero
+@findex cabs
+@findex cabsf
+@findex cabsl
+@findex cacos
+@findex cacosf
+@findex cacosh
+@findex cacoshf
+@findex cacoshl
+@findex cacosl
+@findex calloc
+@findex carg
+@findex cargf
+@findex cargl
+@findex casin
+@findex casinf
+@findex casinh
+@findex casinhf
+@findex casinhl
+@findex casinl
+@findex catan
+@findex catanf
+@findex catanh
+@findex catanhf
+@findex catanhl
+@findex catanl
+@findex cbrt
+@findex cbrtf
+@findex cbrtl
+@findex ccos
+@findex ccosf
+@findex ccosh
+@findex ccoshf
+@findex ccoshl
+@findex ccosl
@findex ceil
@findex ceilf
@findex ceill
+@findex cexp
+@findex cexpf
+@findex cexpl
@findex cimag
@findex cimagf
@findex cimagl
@findex conj
@findex conjf
@findex conjl
+@findex copysign
+@findex copysignf
+@findex copysignl
@findex cos
@findex cosf
+@findex cosh
+@findex coshf
+@findex coshl
@findex cosl
+@findex cpow
+@findex cpowf
+@findex cpowl
+@findex cproj
+@findex cprojf
+@findex cprojl
@findex creal
@findex crealf
@findex creall
+@findex csin
+@findex csinf
+@findex csinh
+@findex csinhf
+@findex csinhl
+@findex csinl
+@findex csqrt
+@findex csqrtf
+@findex csqrtl
+@findex ctan
+@findex ctanf
+@findex ctanh
+@findex ctanhf
+@findex ctanhl
+@findex ctanl
+@findex dcgettext
+@findex dgettext
+@findex drem
+@findex dremf
+@findex dreml
+@findex erf
+@findex erfc
+@findex erfcf
+@findex erfcl
+@findex erff
+@findex erfl
@findex exit
-@findex _exit
-@findex _Exit
@findex exp
+@findex exp10
+@findex exp10f
+@findex exp10l
+@findex exp2
+@findex exp2f
+@findex exp2l
@findex expf
@findex expl
+@findex expm1
+@findex expm1f
+@findex expm1l
@findex fabs
@findex fabsf
@findex fabsl
+@findex fdim
+@findex fdimf
+@findex fdiml
@findex ffs
@findex floor
@findex floorf
@findex floorl
+@findex fma
+@findex fmaf
+@findex fmal
+@findex fmax
+@findex fmaxf
+@findex fmaxl
+@findex fmin
+@findex fminf
+@findex fminl
@findex fmod
@findex fmodf
@findex fmodl
@findex fprintf_unlocked
@findex fputs
@findex fputs_unlocked
+@findex frexp
+@findex frexpf
+@findex frexpl
+@findex fscanf
+@findex gamma
+@findex gammaf
+@findex gammal
+@findex gettext
+@findex hypot
+@findex hypotf
+@findex hypotl
+@findex ilogb
+@findex ilogbf
+@findex ilogbl
@findex imaxabs
@findex index
+@findex j0
+@findex j0f
+@findex j0l
+@findex j1
+@findex j1f
+@findex j1l
+@findex jn
+@findex jnf
+@findex jnl
@findex labs
+@findex ldexp
+@findex ldexpf
+@findex ldexpl
+@findex lgamma
+@findex lgammaf
+@findex lgammal
@findex llabs
+@findex llrint
+@findex llrintf
+@findex llrintl
+@findex llround
+@findex llroundf
+@findex llroundl
@findex log
+@findex log10
+@findex log10f
+@findex log10l
+@findex log1p
+@findex log1pf
+@findex log1pl
+@findex log2
+@findex log2f
+@findex log2l
+@findex logb
+@findex logbf
+@findex logbl
@findex logf
@findex logl
+@findex lrint
+@findex lrintf
+@findex lrintl
+@findex lround
+@findex lroundf
+@findex lroundl
+@findex malloc
@findex memcmp
@findex memcpy
+@findex mempcpy
@findex memset
+@findex modf
+@findex modff
+@findex modfl
@findex nearbyint
@findex nearbyintf
@findex nearbyintl
+@findex nextafter
+@findex nextafterf
+@findex nextafterl
+@findex nexttoward
+@findex nexttowardf
+@findex nexttowardl
@findex pow
+@findex pow10
+@findex pow10f
+@findex pow10l
@findex powf
@findex powl
@findex printf
@findex printf_unlocked
@findex putchar
@findex puts
+@findex remainder
+@findex remainderf
+@findex remainderl
+@findex remquo
+@findex remquof
+@findex remquol
@findex rindex
+@findex rint
+@findex rintf
+@findex rintl
@findex round
@findex roundf
@findex roundl
-@findex scanf
+@findex scalb
+@findex scalbf
+@findex scalbl
+@findex scalbln
+@findex scalblnf
+@findex scalblnf
+@findex scalbn
+@findex scalbnf
+@findex scanfnl
+@findex signbit
+@findex signbitf
+@findex signbitl
+@findex significand
+@findex significandf
+@findex significandl
@findex sin
+@findex sincos
+@findex sincosf
+@findex sincosl
@findex sinf
+@findex sinh
+@findex sinhf
+@findex sinhl
@findex sinl
@findex snprintf
@findex sprintf
@findex sqrtf
@findex sqrtl
@findex sscanf
+@findex stpcpy
@findex strcat
@findex strchr
@findex strcmp
@findex strcpy
@findex strcspn
+@findex strdup
+@findex strfmon
+@findex strftime
@findex strlen
@findex strncat
@findex strncmp
@findex strrchr
@findex strspn
@findex strstr
+@findex tan
+@findex tanf
+@findex tanh
+@findex tanhf
+@findex tanhl
+@findex tanl
+@findex tgamma
+@findex tgammaf
+@findex tgammal
@findex trunc
@findex truncf
@findex truncl
+@findex vfprintf
+@findex vfscanf
@findex vprintf
@findex vscanf
@findex vsnprintf
@findex vsprintf
@findex vsscanf
+@findex y0
+@findex y0f
+@findex y0l
+@findex y1
+@findex y1f
+@findex y1l
+@findex yn
+@findex ynf
+@findex ynl
GCC provides a large number of built-in functions other than the ones
mentioned above. Some of these are for internal use in the processing
@opindex ansi
@opindex std
Outside strict ISO C mode (@option{-ansi}, @option{-std=c89} or
-@option{-std=c99}), the functions @code{alloca}, @code{bcmp},
-@code{bzero}, @code{_exit}, @code{ffs}, @code{fprintf_unlocked},
-@code{fputs_unlocked}, @code{index}, @code{printf_unlocked},
-and @code{rindex} may be handled as built-in functions.
+@option{-std=c99}), the functions
+@code{_exit}, @code{alloca}, @code{bcmp}, @code{bzero},
+@code{dcgettext}, @code{dgettext}, @code{dremf}, @code{dreml},
+@code{drem}, @code{exp10f}, @code{exp10l}, @code{exp10}, @code{ffsll},
+@code{ffsl}, @code{ffs}, @code{fprintf_unlocked}, @code{fputs_unlocked},
+@code{gammaf}, @code{gammal}, @code{gamma}, @code{gettext},
+@code{index}, @code{j0f}, @code{j0l}, @code{j0}, @code{j1f}, @code{j1l},
+@code{j1}, @code{jnf}, @code{jnl}, @code{jn}, @code{mempcpy},
+@code{pow10f}, @code{pow10l}, @code{pow10}, @code{printf_unlocked},
+@code{rindex}, @code{scalbf}, @code{scalbl}, @code{scalb},
+@code{signbit}, @code{signbitf}, @code{signbitl},
+@code{significandf}, @code{significandl}, @code{significand},
+@code{sincosf}, @code{sincosl}, @code{sincos}, @code{stpcpy},
+@code{strdup}, @code{strfmon}, @code{y0f}, @code{y0l}, @code{y0},
+@code{y1f}, @code{y1l}, @code{y1}, @code{ynf}, @code{ynl} and @code{yn}
+may be handled as built-in functions.
All these functions have corresponding versions
prefixed with @code{__builtin_}, which may be used even in strict C89
mode.
-The ISO C99 functions @code{conj}, @code{conjf}, @code{conjl}, @code{creal},
-@code{crealf}, @code{creall}, @code{cimag}, @code{cimagf}, @code{cimagl},
-@code{_Exit}, @code{imaxabs}, @code{llabs},
-@code{nearbyint}, @code{nearbyintf}, @code{nearbyintl},
-@code{round}, @code{roundf}, @code{roundl}, @code{snprintf},
-@code{trunc}, @code{truncf}, @code{truncl},
-@code{vscanf}, @code{vsnprintf} and @code{vsscanf}
+The ISO C99 functions
+@code{_Exit}, @code{acoshf}, @code{acoshl}, @code{acosh}, @code{asinhf},
+@code{asinhl}, @code{asinh}, @code{atanhf}, @code{atanhl}, @code{atanh},
+@code{cabsf}, @code{cabsl}, @code{cabs}, @code{cacosf}, @code{cacoshf},
+@code{cacoshl}, @code{cacosh}, @code{cacosl}, @code{cacos},
+@code{cargf}, @code{cargl}, @code{carg}, @code{casinf}, @code{casinhf},
+@code{casinhl}, @code{casinh}, @code{casinl}, @code{casin},
+@code{catanf}, @code{catanhf}, @code{catanhl}, @code{catanh},
+@code{catanl}, @code{catan}, @code{cbrtf}, @code{cbrtl}, @code{cbrt},
+@code{ccosf}, @code{ccoshf}, @code{ccoshl}, @code{ccosh}, @code{ccosl},
+@code{ccos}, @code{cexpf}, @code{cexpl}, @code{cexp}, @code{cimagf},
+@code{cimagl}, @code{cimag},
+@code{conjf}, @code{conjl}, @code{conj}, @code{copysignf},
+@code{copysignl}, @code{copysign}, @code{cpowf}, @code{cpowl},
+@code{cpow}, @code{cprojf}, @code{cprojl}, @code{cproj}, @code{crealf},
+@code{creall}, @code{creal}, @code{csinf}, @code{csinhf}, @code{csinhl},
+@code{csinh}, @code{csinl}, @code{csin}, @code{csqrtf}, @code{csqrtl},
+@code{csqrt}, @code{ctanf}, @code{ctanhf}, @code{ctanhl}, @code{ctanh},
+@code{ctanl}, @code{ctan}, @code{erfcf}, @code{erfcl}, @code{erfc},
+@code{erff}, @code{erfl}, @code{erf}, @code{exp2f}, @code{exp2l},
+@code{exp2}, @code{expm1f}, @code{expm1l}, @code{expm1}, @code{fdimf},
+@code{fdiml}, @code{fdim}, @code{fmaf}, @code{fmal}, @code{fmaxf},
+@code{fmaxl}, @code{fmax}, @code{fma}, @code{fminf}, @code{fminl},
+@code{fmin}, @code{hypotf}, @code{hypotl}, @code{hypot}, @code{ilogbf},
+@code{ilogbl}, @code{ilogb}, @code{imaxabs}, @code{lgammaf},
+@code{lgammal}, @code{lgamma}, @code{llabs}, @code{llrintf},
+@code{llrintl}, @code{llrint}, @code{llroundf}, @code{llroundl},
+@code{llround}, @code{log1pf}, @code{log1pl}, @code{log1p},
+@code{log2f}, @code{log2l}, @code{log2}, @code{logbf}, @code{logbl},
+@code{logb}, @code{lrintf}, @code{lrintl}, @code{lrint}, @code{lroundf},
+@code{lroundl}, @code{lround}, @code{nearbyintf}, @code{nearbyintl},
+@code{nearbyint}, @code{nextafterf}, @code{nextafterl},
+@code{nextafter}, @code{nexttowardf}, @code{nexttowardl},
+@code{nexttoward}, @code{remainderf}, @code{remainderl},
+@code{remainder}, @code{remquof}, @code{remquol}, @code{remquo},
+@code{rintf}, @code{rintl}, @code{rint}, @code{roundf}, @code{roundl},
+@code{round}, @code{scalblnf}, @code{scalblnl}, @code{scalbln},
+@code{scalbnf}, @code{scalbnl}, @code{scalbn}, @code{snprintf},
+@code{tgammaf}, @code{tgammal}, @code{tgamma}, @code{truncf},
+@code{truncl}, @code{trunc}, @code{vfscanf}, @code{vscanf},
+@code{vsnprintf} and @code{vsscanf}
are handled as built-in functions
except in strict ISO C90 mode (@option{-ansi} or @option{-std=c89}).
-There are also built-in versions of the ISO C99 functions @code{atan2f},
-@code{atan2l}, @code{ceilf}, @code{ceill}, @code{cosf}, @code{cosl},
-@code{expf}, @code{expl}, @code{fabsf}, @code{fabsl}, @code{floorf},
-@code{floorl}, @code{fmodf}, @code{fmodl},
-@code{logf}, @code{logl}, @code{powf}, @code{powl},
-@code{sinf}, @code{sinl}, @code{sqrtf} and @code{sqrtl}
+There are also built-in versions of the ISO C99 functions
+@code{acosf}, @code{acosl}, @code{asinf}, @code{asinl}, @code{atan2f},
+@code{atan2l}, @code{atanf}, @code{atanl}, @code{ceilf}, @code{ceill},
+@code{cosf}, @code{coshf}, @code{coshl}, @code{cosl}, @code{expf},
+@code{expl}, @code{fabsf}, @code{fabsl}, @code{floorf}, @code{floorl},
+@code{fmodf}, @code{fmodl}, @code{frexpf}, @code{frexpl}, @code{ldexpf},
+@code{ldexpl}, @code{log10f}, @code{log10l}, @code{logf}, @code{logl},
+@code{modfl}, @code{modf}, @code{powf}, @code{powl}, @code{sinf},
+@code{sinhf}, @code{sinhl}, @code{sinl}, @code{sqrtf}, @code{sqrtl},
+@code{tanf}, @code{tanhf}, @code{tanhl} and @code{tanl}
that are recognized in any mode since ISO C90 reserves these names for
the purpose to which ISO C99 puts them. All these functions have
corresponding versions prefixed with @code{__builtin_}.
-The ISO C90 functions @code{abort}, @code{abs}, @code{atan2}, @code{ceil},
-@code{cos}, @code{exit},
-@code{exp}, @code{fabs}, @code{floor}, @code{fmod},
-@code{fprintf}, @code{fputs}, @code{labs}, @code{log},
-@code{memcmp}, @code{memcpy}, @code{memset}, @code{pow}, @code{printf},
-@code{putchar}, @code{puts}, @code{scanf}, @code{sin}, @code{snprintf},
-@code{sprintf}, @code{sqrt}, @code{sscanf},
-@code{strcat}, @code{strchr}, @code{strcmp},
-@code{strcpy}, @code{strcspn}, @code{strlen}, @code{strncat}, @code{strncmp},
-@code{strncpy}, @code{strpbrk}, @code{strrchr}, @code{strspn}, @code{strstr},
-@code{vprintf} and @code{vsprintf}
+The ISO C90 functions
+@code{abort}, @code{abs}, @code{acos}, @code{asin}, @code{atan2},
+@code{atan}, @code{calloc}, @code{ceil}, @code{cosh}, @code{cos},
+@code{exit}, @code{exp}, @code{fabs}, @code{floor}, @code{fmod},
+@code{fprintf}, @code{fputs}, @code{frexp}, @code{fscanf}, @code{labs},
+@code{ldexp}, @code{log10}, @code{log}, @code{malloc}, @code{memcmp},
+@code{memcpy}, @code{memset}, @code{modf}, @code{pow}, @code{printf},
+@code{putchar}, @code{puts}, @code{scanf}, @code{sinh}, @code{sin},
+@code{snprintf}, @code{sprintf}, @code{sqrt}, @code{sscanf},
+@code{strcat}, @code{strchr}, @code{strcmp}, @code{strcpy},
+@code{strcspn}, @code{strlen}, @code{strncat}, @code{strncmp},
+@code{strncpy}, @code{strpbrk}, @code{strrchr}, @code{strspn},
+@code{strstr}, @code{tanh}, @code{tan}, @code{vfprintf}, @code{vprintf}
+and @code{vsprintf}
are all recognized as built-in functions unless
@option{-fno-builtin} is specified (or @option{-fno-builtin-@var{function}}
is specified for an individual function). All of these functions have
@code{short **}. Furthermore, two types that are typedefed are
considered compatible if their underlying types are compatible.
-An @code{enum} type is considered to be compatible with another
-@code{enum} type. For example, @code{enum @{foo, bar@}} is similar to
+An @code{enum} type is not considered to be compatible with another
+@code{enum} type even if both are compatible with the same integer
+type; this is what the C standard specifies.
+For example, @code{enum @{foo, bar@}} is not similar to
@code{enum @{hot, dog@}}.
You would typically use this function in code whose execution varies
Similar to @code{__builtin_huge_val}, except the return type is @code{float}.
@end deftypefn
-@deftypefn {Built-in Function} long double __builtin_huge_vall (void)
+@deftypefn {Built-in Function} {long double} __builtin_huge_vall (void)
Similar to @code{__builtin_huge_val}, except the return
type is @code{long double}.
@end deftypefn
Similar to @code{__builtin_inf}, except the return type is @code{float}.
@end deftypefn
-@deftypefn {Built-in Function} long double __builtin_infl (void)
+@deftypefn {Built-in Function} {long double} __builtin_infl (void)
Similar to @code{__builtin_inf}, except the return
type is @code{long double}.
@end deftypefn
is parsed as by @code{strtol}; that is, the base is recognized by
leading @samp{0} or @samp{0x} prefixes. The number parsed is placed
in the significand such that the least significant bit of the number
-is at the least significant bit of the significand. The number is
+is at the least significant bit of the significand. The number is
truncated to fit the significand field provided. The significand is
forced to be a quiet NaN.
Similar to @code{__builtin_nan}, except the return type is @code{float}.
@end deftypefn
-@deftypefn {Built-in Function} long double __builtin_nanl (const char *str)
+@deftypefn {Built-in Function} {long double} __builtin_nanl (const char *str)
Similar to @code{__builtin_nan}, except the return type is @code{long double}.
@end deftypefn
@deftypefn {Built-in Function} double __builtin_nans (const char *str)
-Similar to @code{__builtin_nan}, except the significand is forced
+Similar to @code{__builtin_nan}, except the significand is forced
to be a signaling NaN. The @code{nans} function is proposed by
@uref{http://std.dkuug.dk/JTC1/SC22/WG14/www/docs/n965.htm,,WG14 N965}.
@end deftypefn
Similar to @code{__builtin_nans}, except the return type is @code{float}.
@end deftypefn
-@deftypefn {Built-in Function} long double __builtin_nansl (const char *str)
+@deftypefn {Built-in Function} {long double} __builtin_nansl (const char *str)
Similar to @code{__builtin_nans}, except the return type is @code{long double}.
@end deftypefn
@menu
* Alpha Built-in Functions::
+* ARM Built-in Functions::
* X86 Built-in Functions::
* PowerPC AltiVec Built-in Functions::
@end menu
The following built-in functions are always available. They
all generate the machine instruction that is part of the name.
-@example
+@smallexample
long __builtin_alpha_implver (void)
long __builtin_alpha_rpcc (void)
long __builtin_alpha_amask (long)
long __builtin_alpha_umulh (long, long)
long __builtin_alpha_zap (long, long)
long __builtin_alpha_zapnot (long, long)
-@end example
+@end smallexample
The following built-in functions are always with @option{-mmax}
or @option{-mcpu=@var{cpu}} where @var{cpu} is @code{pca56} or
later. They all generate the machine instruction that is part
of the name.
-@example
+@smallexample
long __builtin_alpha_pklb (long)
long __builtin_alpha_pkwb (long)
long __builtin_alpha_unpkbl (long)
long __builtin_alpha_maxuw4 (long, long)
long __builtin_alpha_maxsw4 (long, long)
long __builtin_alpha_perr (long, long)
-@end example
+@end smallexample
The following built-in functions are always with @option{-mcix}
or @option{-mcpu=@var{cpu}} where @var{cpu} is @code{ev67} or
later. They all generate the machine instruction that is part
of the name.
-@example
+@smallexample
long __builtin_alpha_cttz (long)
long __builtin_alpha_ctlz (long)
long __builtin_alpha_ctpop (long)
-@end example
+@end smallexample
The following builtins are available on systems that use the OSF/1
PALcode. Normally they invoke the @code{rduniq} and @code{wruniq}
PAL calls, but when invoked with @option{-mtls-kernel}, they invoke
@code{rdval} and @code{wrval}.
-@example
+@smallexample
void *__builtin_thread_pointer (void)
void __builtin_set_thread_pointer (void *)
-@end example
+@end smallexample
+
+@node ARM Built-in Functions
+@subsection ARM Built-in Functions
+
+These built-in functions are available for the ARM family of
+processors, when the @option{-mcpu=iwmmxt} switch is used:
+
+@smallexample
+typedef int __v2si __attribute__ ((__mode__ (__V2SI__)))
+
+v2si __builtin_arm_waddw (v2si, v2si)
+v2si __builtin_arm_waddw (v2si, v2si)
+v2si __builtin_arm_wsubw (v2si, v2si)
+v2si __builtin_arm_wsubw (v2si, v2si)
+v2si __builtin_arm_waddwss (v2si, v2si)
+v2si __builtin_arm_wsubwss (v2si, v2si)
+v2si __builtin_arm_wsubwss (v2si, v2si)
+v2si __builtin_arm_wsubwss (v2si, v2si)
+v2si __builtin_arm_wsubwss (v2si, v2si)
+v2si __builtin_arm_waddwus (v2si, v2si)
+v2si __builtin_arm_wsubwus (v2si, v2si)
+v2si __builtin_arm_wsubwus (v2si, v2si)
+v2si __builtin_arm_wmaxuw (v2si, v2si)
+v2si __builtin_arm_wmaxsw (v2si, v2si)
+v2si __builtin_arm_wavg2br (v2si, v2si)
+v2si __builtin_arm_wavg2hr (v2si, v2si)
+v2si __builtin_arm_wavg2b (v2si, v2si)
+v2si __builtin_arm_wavg2h (v2si, v2si)
+v2si __builtin_arm_waccb (v2si)
+v2si __builtin_arm_wacch (v2si)
+v2si __builtin_arm_waccw (v2si)
+v2si __builtin_arm_wmacs (v2si, v2si, v2si)
+v2si __builtin_arm_wmacsz (v2si, v2si, v2si)
+v2si __builtin_arm_wmacu (v2si, v2si, v2si)
+v2si __builtin_arm_wmacuz (v2si, v2si)
+v2si __builtin_arm_wsadb (v2si, v2si)
+v2si __builtin_arm_wsadbz (v2si, v2si)
+v2si __builtin_arm_wsadh (v2si, v2si)
+v2si __builtin_arm_wsadhz (v2si, v2si)
+v2si __builtin_arm_walign (v2si, v2si)
+v2si __builtin_arm_tmia (v2si, int, int)
+v2si __builtin_arm_tmiaph (v2si, int, int)
+v2si __builtin_arm_tmiabb (v2si, int, int)
+v2si __builtin_arm_tmiabt (v2si, int, int)
+v2si __builtin_arm_tmiatb (v2si, int, int)
+v2si __builtin_arm_tmiatt (v2si, int, int)
+int __builtin_arm_tmovmskb (v2si)
+int __builtin_arm_tmovmskh (v2si)
+int __builtin_arm_tmovmskw (v2si)
+v2si __builtin_arm_wmadds (v2si, v2si)
+v2si __builtin_arm_wmaddu (v2si, v2si)
+v2si __builtin_arm_wpackhss (v2si, v2si)
+v2si __builtin_arm_wpackwss (v2si, v2si)
+v2si __builtin_arm_wpackdss (v2si, v2si)
+v2si __builtin_arm_wpackhus (v2si, v2si)
+v2si __builtin_arm_wpackwus (v2si, v2si)
+v2si __builtin_arm_wpackdus (v2si, v2si)
+v2si __builtin_arm_waddb (v2si, v2si)
+v2si __builtin_arm_waddh (v2si, v2si)
+v2si __builtin_arm_waddw (v2si, v2si)
+v2si __builtin_arm_waddbss (v2si, v2si)
+v2si __builtin_arm_waddhss (v2si, v2si)
+v2si __builtin_arm_waddwss (v2si, v2si)
+v2si __builtin_arm_waddbus (v2si, v2si)
+v2si __builtin_arm_waddhus (v2si, v2si)
+v2si __builtin_arm_waddwus (v2si, v2si)
+v2si __builtin_arm_wsubb (v2si, v2si)
+v2si __builtin_arm_wsubh (v2si, v2si)
+v2si __builtin_arm_wsubw (v2si, v2si)
+v2si __builtin_arm_wsubbss (v2si, v2si)
+v2si __builtin_arm_wsubhss (v2si, v2si)
+v2si __builtin_arm_wsubwss (v2si, v2si)
+v2si __builtin_arm_wsubbus (v2si, v2si)
+v2si __builtin_arm_wsubhus (v2si, v2si)
+v2si __builtin_arm_wsubwus (v2si, v2si)
+v2si __builtin_arm_wand (v2si, v2si)
+v2si __builtin_arm_wandn (v2si, v2si)
+v2si __builtin_arm_wor (v2si, v2si)
+v2si __builtin_arm_wxor (v2si, v2si)
+v2si __builtin_arm_wcmpeqb (v2si, v2si)
+v2si __builtin_arm_wcmpeqh (v2si, v2si)
+v2si __builtin_arm_wcmpeqw (v2si, v2si)
+v2si __builtin_arm_wcmpgtub (v2si, v2si)
+v2si __builtin_arm_wcmpgtuh (v2si, v2si)
+v2si __builtin_arm_wcmpgtuw (v2si, v2si)
+v2si __builtin_arm_wcmpgtsb (v2si, v2si)
+v2si __builtin_arm_wcmpgtsh (v2si, v2si)
+v2si __builtin_arm_wcmpgtsw (v2si, v2si)
+int __builtin_arm_textrmsb (v2si, int)
+int __builtin_arm_textrmsh (v2si, int)
+int __builtin_arm_textrmsw (v2si, int)
+int __builtin_arm_textrmub (v2si, int)
+int __builtin_arm_textrmuh (v2si, int)
+int __builtin_arm_textrmuw (v2si, int)
+v2si __builtin_arm_tinsrb (v2si, int, int)
+v2si __builtin_arm_tinsrh (v2si, int, int)
+v2si __builtin_arm_tinsrw (v2si, int, int)
+v2si __builtin_arm_wmaxsw (v2si, v2si)
+v2si __builtin_arm_wmaxsh (v2si, v2si)
+v2si __builtin_arm_wmaxsb (v2si, v2si)
+v2si __builtin_arm_wmaxuw (v2si, v2si)
+v2si __builtin_arm_wmaxuh (v2si, v2si)
+v2si __builtin_arm_wmaxub (v2si, v2si)
+v2si __builtin_arm_wminsw (v2si, v2si)
+v2si __builtin_arm_wminsh (v2si, v2si)
+v2si __builtin_arm_wminsb (v2si, v2si)
+v2si __builtin_arm_wminuw (v2si, v2si)
+v2si __builtin_arm_wminuh (v2si, v2si)
+v2si __builtin_arm_wminub (v2si, v2si)
+v2si __builtin_arm_wmuluh (v2si, v2si)
+v2si __builtin_arm_wmulsh (v2si, v2si)
+v2si __builtin_arm_wmulul (v2si, v2si)
+v2si __builtin_arm_wshufh (v2si, int)
+v2si __builtin_arm_wsllh (v2si, v2si)
+v2si __builtin_arm_wsllw (v2si, v2si)
+v2si __builtin_arm_wslld (v2si, v2si)
+v2si __builtin_arm_wsrah (v2si, v2si)
+v2si __builtin_arm_wsraw (v2si, v2si)
+v2si __builtin_arm_wsrad (v2si, v2si)
+v2si __builtin_arm_wsrlh (v2si, v2si)
+v2si __builtin_arm_wsrlw (v2si, v2si)
+v2si __builtin_arm_wsrld (v2si, v2si)
+v2si __builtin_arm_wrorh (v2si, v2si)
+v2si __builtin_arm_wrorw (v2si, v2si)
+v2si __builtin_arm_wrord (v2si, v2si)
+v2si __builtin_arm_wsllhi (v2si, int)
+v2si __builtin_arm_wsllwi (v2si, int)
+v2si __builtin_arm_wslldi (v2si, v2si)
+v2si __builtin_arm_wsrahi (v2si, int)
+v2si __builtin_arm_wsrawi (v2si, int)
+v2si __builtin_arm_wsradi (v2si, v2si)
+v2si __builtin_arm_wsrlwi (v2si, int)
+v2si __builtin_arm_wsrldi (v2si, int)
+v2si __builtin_arm_wrorhi (v2si, int)
+v2si __builtin_arm_wrorwi (v2si, int)
+v2si __builtin_arm_wrordi (v2si, int)
+v2si __builtin_arm_wunpckihb (v2si, v2si)
+v2si __builtin_arm_wunpckihh (v2si, v2si)
+v2si __builtin_arm_wunpckihw (v2si, v2si)
+v2si __builtin_arm_wunpckilb (v2si, v2si)
+v2si __builtin_arm_wunpckilh (v2si, v2si)
+v2si __builtin_arm_wunpckilw (v2si, v2si)
+v2si __builtin_arm_wunpckehsb (v2si)
+v2si __builtin_arm_wunpckehsh (v2si)
+v2si __builtin_arm_wunpckehsw (v2si)
+v2si __builtin_arm_wunpckehub (v2si)
+v2si __builtin_arm_wunpckehuh (v2si)
+v2si __builtin_arm_wunpckehuw (v2si)
+v2si __builtin_arm_wunpckelsb (v2si)
+v2si __builtin_arm_wunpckelsh (v2si)
+v2si __builtin_arm_wunpckelsw (v2si)
+v2si __builtin_arm_wunpckelub (v2si)
+v2si __builtin_arm_wunpckeluh (v2si)
+v2si __builtin_arm_wunpckeluw (v2si)
+v2si __builtin_arm_wsubwss (v2si, v2si)
+v2si __builtin_arm_wsraw (v2si, v2si)
+v2si __builtin_arm_wsrad (v2si, v2si)
+@end smallexample
@node X86 Built-in Functions
@subsection X86 Built-in Functions
The following built-in functions are made available by @option{-mmmx}.
All of them generate the machine instruction that is part of the name.
-@example
+@smallexample
v8qi __builtin_ia32_paddb (v8qi, v8qi)
v4hi __builtin_ia32_paddw (v4hi, v4hi)
v2si __builtin_ia32_paddd (v2si, v2si)
v8qi __builtin_ia32_packsswb (v4hi, v4hi)
v4hi __builtin_ia32_packssdw (v2si, v2si)
v8qi __builtin_ia32_packuswb (v4hi, v4hi)
-@end example
+@end smallexample
The following built-in functions are made available either with
@option{-msse}, or with a combination of @option{-m3dnow} and
@option{-march=athlon}. All of them generate the machine
instruction that is part of the name.
-@example
+@smallexample
v4hi __builtin_ia32_pmulhuw (v4hi, v4hi)
v8qi __builtin_ia32_pavgb (v8qi, v8qi)
v4hi __builtin_ia32_pavgw (v4hi, v4hi)
void __builtin_ia32_maskmovq (v8qi, v8qi, char *)
void __builtin_ia32_movntq (di *, di)
void __builtin_ia32_sfence (void)
-@end example
+@end smallexample
The following built-in functions are available when @option{-msse} is used.
All of them generate the machine instruction that is part of the name.
-@example
+@smallexample
int __builtin_ia32_comieq (v4sf, v4sf)
int __builtin_ia32_comineq (v4sf, v4sf)
int __builtin_ia32_comilt (v4sf, v4sf)
v4sf __builtin_ia32_shufps (v4sf, v4sf, int)
void __builtin_ia32_movntps (float *, v4sf)
int __builtin_ia32_movmskps (v4sf)
-@end example
+@end smallexample
The following built-in functions are available when @option{-msse} is used.
Generates the @code{movlps} machine instruction as a store to memory.
@end table
+The following built-in functions are available when @option{-mpni} is used.
+All of them generate the machine instruction that is part of the name.
+
+@smallexample
+v2df __builtin_ia32_addsubpd (v2df, v2df)
+v2df __builtin_ia32_addsubps (v2df, v2df)
+v2df __builtin_ia32_haddpd (v2df, v2df)
+v2df __builtin_ia32_haddps (v2df, v2df)
+v2df __builtin_ia32_hsubpd (v2df, v2df)
+v2df __builtin_ia32_hsubps (v2df, v2df)
+v16qi __builtin_ia32_lddqu (char const *)
+void __builtin_ia32_monitor (void *, unsigned int, unsigned int)
+v2df __builtin_ia32_movddup (v2df)
+v4sf __builtin_ia32_movshdup (v4sf)
+v4sf __builtin_ia32_movsldup (v4sf)
+void __builtin_ia32_mwait (unsigned int, unsigned int)
+@end smallexample
+
+The following built-in functions are available when @option{-mpni} is used.
+
+@table @code
+@item v2df __builtin_ia32_loadddup (double const *)
+Generates the @code{movddup} machine instruction as a load from memory.
+@end table
+
The following built-in functions are available when @option{-m3dnow} is used.
All of them generate the machine instruction that is part of the name.
-@example
+@smallexample
void __builtin_ia32_femms (void)
v8qi __builtin_ia32_pavgusb (v8qi, v8qi)
v2si __builtin_ia32_pf2id (v2sf)
v2sf __builtin_ia32_pfsubr (v2sf, v2sf)
v2sf __builtin_ia32_pi2fd (v2si)
v4hi __builtin_ia32_pmulhrw (v4hi, v4hi)
-@end example
+@end smallexample
The following built-in functions are available when both @option{-m3dnow}
and @option{-march=athlon} are used. All of them generate the machine
instruction that is part of the name.
-@example
+@smallexample
v2si __builtin_ia32_pf2iw (v2sf)
v2sf __builtin_ia32_pfnacc (v2sf, v2sf)
v2sf __builtin_ia32_pfpnacc (v2sf, v2sf)
v2sf __builtin_ia32_pi2fw (v2si)
v2sf __builtin_ia32_pswapdsf (v2sf)
v2si __builtin_ia32_pswapdsi (v2si)
-@end example
+@end smallexample
@node PowerPC AltiVec Built-in Functions
@subsection PowerPC AltiVec Built-in Functions
a structure or union that contains, as fields, structures and unions
without names. For example:
-@example
+@smallexample
struct @{
int a;
union @{
@};
int d;
@} foo;
-@end example
+@end smallexample
In this example, the user would be able to access members of the unnamed
union with code like @samp{foo.b}. Note that only unnamed structs and
You must never create such structures that cause ambiguous field definitions.
For example, this structure:
-@example
+@smallexample
struct @{
int a;
struct @{
int a;
@};
@} foo;
-@end example
+@end smallexample
It is ambiguous which @code{a} is being referred to with @samp{foo.a}.
Such constructs are not supported and must be avoided. In the future,
At the user level, the extension is visible with a new storage
class keyword: @code{__thread}. For example:
-@example
+@smallexample
__thread int i;
extern __thread struct state s;
static __thread char *p;
-@end example
+@end smallexample
The @code{__thread} specifier may be used alone, with the @code{extern}
or @code{static} specifiers, but with no other storage class specifier.
New section before @b{[basic.stc.static]}
@quotation
-The keyword @code{__thread} applied to an non-local object gives the
+The keyword @code{__thread} applied to a non-local object gives the
object thread storage duration.
A local variable or class data member declared both @code{static}
want to write code that checks whether these features are available, you can
test for the GNU compiler the same way as for C programs: check for a
predefined macro @code{__GNUC__}. You can also use @code{__GNUG__} to
-test specifically for GNU C++ (@pxref{Standard Predefined,,Standard
-Predefined Macros,cpp.info,The C Preprocessor}).
+test specifically for GNU C++ (@pxref{Common Predefined Macros,,
+Predefined Macros,cpp,The GNU C Preprocessor}).
@menu
* Min and Max:: C++ Minimum and maximum operators.
* Bound member functions:: You can extract a function pointer to the
method denoted by a @samp{->*} or @samp{.*} expression.
* C++ Attributes:: Variable, function, and type attributes for C++ only.
+* Strong Using:: Strong using-directives for namespace composition.
+* Offsetof:: Special syntax for implementing @code{offsetof}.
* Java Exceptions:: Tweaking exception handling to work with Java.
-* Deprecated Features:: Things might disappear from g++.
+* Deprecated Features:: Things will disappear from g++.
* Backwards Compatibility:: Compatibilities with earlier definitions of C++.
@end menu
use a macro to return the minimum of two things in C++, as in the
following example.
-@example
+@smallexample
#define MIN(X,Y) ((X) < (Y) ? : (X) : (Y))
-@end example
+@end smallexample
@noindent
You might then use @w{@samp{int min = MIN (i, j);}} to set @var{min} to
In most expressions, it is intuitively obvious what is a read and what is
a write. For instance
-@example
+@smallexample
volatile int *dst = @var{somevalue};
volatile int *src = @var{someothervalue};
*dst = *src;
-@end example
+@end smallexample
@noindent
will cause a read of the volatile object pointed to by @var{src} and stores the
Less obvious expressions are where something which looks like an access
is used in a void context. An example would be,
-@example
+@smallexample
volatile int *src = @var{somevalue};
*src;
-@end example
+@end smallexample
With C, such expressions are rvalues, and as rvalues cause a read of
the object, GCC interprets this as a read of the volatile being pointed
of the object. When the object has incomplete type, G++ issues a
warning.
-@example
+@smallexample
struct S;
struct T @{int m;@};
volatile S *ptr1 = @var{somevalue};
volatile T *ptr2 = @var{somevalue};
*ptr1;
*ptr2;
-@end example
+@end smallexample
In this example, a warning is issued for @code{*ptr1}, and @code{*ptr2}
causes a read of the object pointed to. If you wish to force an error on
references, which indicate that the reference is not aliased in the local
context.
-@example
+@smallexample
void fn (int *__restrict__ rptr, int &__restrict__ rref)
@{
/* @r{@dots{}} */
@}
-@end example
+@end smallexample
@noindent
In the body of @code{fn}, @var{rptr} points to an unaliased integer and
You may also specify whether a member function's @var{this} pointer is
unaliased by using @code{__restrict__} as a member function qualifier.
-@example
+@smallexample
void T::fn () __restrict__
@{
/* @r{@dots{}} */
@}
-@end example
+@end smallexample
@noindent
Within the body of @code{T::fn}, @var{this} will have the effective
@end table
When used with GNU ld version 2.8 or later on an ELF system such as
-Linux/GNU or Solaris 2, or on Microsoft Windows, duplicate copies of
+GNU/Linux or Solaris 2, or on Microsoft Windows, duplicate copies of
these constructs will be discarded at link time. This is known as
COMDAT support.
@end table
When used with GNU ld version 2.8 or later on an ELF system such as
-Linux/GNU or Solaris 2, or on Microsoft Windows, g++ supports the
+GNU/Linux or Solaris 2, or on Microsoft Windows, g++ supports the
Borland model. On other systems, g++ implements neither automatic
model.
instantiations you need into one big file; or you can create small files
like
-@example
+@smallexample
#include "Foo.h"
#include "Foo.cc"
template class Foo<int>;
template ostream& operator <<
(ostream&, const Foo<int>&);
-@end example
+@end smallexample
for each of the instances you need, and create a template instantiation
library from those.
members of a template class, without the support data or member
functions (with (@code{static}):
-@example
+@smallexample
extern template int max (int, int);
inline template class Foo<int>;
static template class Foo<int>;
-@end example
+@end smallexample
@item
Do nothing. Pretend g++ does implement automatic instantiation
The syntax for this extension is
-@example
+@smallexample
extern A a;
extern int (A::*fp)();
typedef int (*fptr)(A *);
fptr p = (fptr)(a.*fp);
-@end example
+@end smallexample
For PMF constants (i.e.@: expressions of the form @samp{&Klasse::Member}),
no object is needed to obtain the address of the function. They can be
converted to function pointers directly:
-@example
+@smallexample
fptr p1 = (fptr)(&A::foo);
-@end example
+@end smallexample
@opindex Wno-pmf-conversions
You must specify @option{-Wno-pmf-conversions} to use this extension.
@end table
+See also @xref{Strong Using}.
+
+@node Strong Using
+@section Strong Using
+
+A using-directive with @code{__attribute ((strong))} is stronger
+than a normal using-directive in two ways:
+
+@itemize @bullet
+@item
+Templates from the used namespace can be specialized as though they were members of the using namespace.
+
+@item
+The using namespace is considered an associated namespace of all
+templates in the used namespace for purposes of argument-dependent
+name lookup.
+@end itemize
+
+This is useful for composing a namespace transparently from
+implementation namespaces. For example:
+
+@smallexample
+namespace std @{
+ namespace debug @{
+ template <class T> struct A @{ @};
+ @}
+ using namespace debug __attribute ((__strong__));
+ template <> struct A<int> @{ @}; // ok to specialize
+
+ template <class T> void f (A<T>);
+@}
+
+int main()
+@{
+ f (std::A<float>()); // lookup finds std::f
+ f (std::A<int>());
+@}
+@end smallexample
+
+@node Offsetof
+@section Offsetof
+
+G++ uses a syntactic extension to implement the @code{offsetof} macro.
+
+In particular:
+
+@smallexample
+ __offsetof__ (expression)
+@end smallexample
+
+is equivalent to the parenthesized expression, except that the
+expression is considered an integral constant expression even if it
+contains certain operators that are not normally permitted in an
+integral constant expression. Users should never use
+@code{__offsetof__} directly; the only valid use of
+@code{__offsetof__} is to implement the @code{offsetof} macro in
+@code{<stddef.h>}.
+
@node Java Exceptions
@section Java Exceptions
Floating and complex non-type template parameters have been deprecated,
and are now removed from g++.
-The implicit typename extension has been deprecated and will be removed
-from g++ at some point. In some cases g++ determines that a dependent
-type such as @code{TPL<T>::X} is a type without needing a
-@code{typename} keyword, contrary to the standard.
+The implicit typename extension has been deprecated and is now
+removed from g++.
+
+The use of default arguments in function pointers, function typedefs and
+and other places where they are not permitted by the standard is
+deprecated and will be removed from a future version of g++.
@node Backwards Compatibility
@section Backwards Compatibility
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