@titlepage
@c @finalout
@title The C Preprocessor
-@subtitle Last revised July 1992
+@subtitle Last revised March 1997
@subtitle for GCC version 2
@author Richard M. Stallman
@page
C Language manual.
@vskip 0pt plus 1filll
-Copyright @copyright{} 1987, 1989, 1991, 1992, 1993, 1994, 1995 Free
+Copyright @copyright{} 1987, 1989, 1991, 1992, 1993, 1994, 1995, 1996, 1997 Free
Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of
C preprocessors vary in some details. This manual discusses the GNU C
preprocessor, the C Compatible Compiler Preprocessor. The GNU C
-preprocessor provides a superset of the features of ANSI Standard C.
+preprocessor provides a superset of the features of ANSI Standard C@.
ANSI Standard C requires the rejection of many harmless constructs commonly
used by today's C programs. Such incompatibility would be inconvenient for
practice the consequences of having strict ANSI Standard C make it
undesirable to do this. @xref{Invocation}.
+The C preprocessor is designed for C-like languages; you may run into
+problems if you apply it to other kinds of languages, because it assumes
+that it is dealing with C@. For example, the C preprocessor sometimes
+outputs extra white space to avoid inadvertent C token concatenation,
+and this may cause problems with other languages.
+
@menu
* Global Actions:: Actions made uniformly on all input files.
* Directives:: General syntax of preprocessing directives.
Sometimes it is necessary to give the inheriting file the same name as
the base file. This is less straightforward.
-For example, suppose an application program uses the system header file
+For example, suppose an application program uses the system header
@file{sys/signal.h}, but the version of @file{/usr/include/sys/signal.h}
on a particular system doesn't do what the application program expects.
It might be convenient to define a ``local'' version, perhaps under the
name @file{/usr/local/include/sys/signal.h}, to override or add to the
one supplied by the system.
-You can do this by using the option @samp{-I.} for compilation, and
+You can do this by compiling with the option @samp{-I.}, and
writing a file @file{sys/signal.h} that does what the application
program expects. But making this file include the standard
@file{sys/signal.h} is not so easy---writing @samp{#include
was found.
Suppose you specify @samp{-I /usr/local/include}, and the list of
-directories to search also includes @file{/usr/include}; and suppose that
-both directories contain a file named @file{sys/signal.h}. Ordinary
+directories to search also includes @file{/usr/include}; and suppose
+both directories contain @file{sys/signal.h}. Ordinary
@samp{#include <sys/signal.h>} finds the file under
@file{/usr/local/include}. If that file contains @samp{#include_next
<sys/signal.h>}, it starts searching after that directory, and finds the
@end example
@noindent
-(This is not the best way to define a ``minimum'' macro in GNU C.
+(This is not the best way to define a ``minimum'' macro in GNU C@.
@xref{Side Effects}, for more information.)
To use a macro that expects arguments, you write the name of the macro
@cindex standard predefined macros
The standard predefined macros are available with the same meanings
-regardless of the machine or operating system on which you are using GNU C.
+regardless of the machine or operating system on which you are using GNU C@.
Their names all start and end with double underscores. Those preceding
@code{__GNUC__} in this table are standardized by ANSI C; the rest are
GNU C extensions.
@item __STDC__
@findex __STDC__
This macro expands to the constant 1, to signify that this is ANSI
-Standard C. (Whether that is actually true depends on what C compiler
+Standard C@. (Whether that is actually true depends on what C compiler
will operate on the output from the preprocessor.)
@item __STDC_VERSION__
@item __GNUC__
@findex __GNUC__
-This macro is defined if and only if this is GNU C. This macro is
+This macro is defined if and only if this is GNU C@. This macro is
defined only when the entire GNU C compiler is in use; if you invoke the
preprocessor directly, @samp{__GNUC__} is undefined. The value
identifies the major version number of GNU CC (@samp{1} for GNU CC
specified when GNU C was invoked. Its definition is the null string.
This macro exists primarily to direct certain GNU header files not to
define certain traditional Unix constructs which are incompatible with
-ANSI C.
+ANSI C@.
@item __BASE_FILE__
@findex __BASE_FILE__
@item __VERSION__
@findex __VERSION__
This macro expands to a string which describes the version number of
-GNU C. The string is normally a sequence of decimal numbers separated
+GNU C@. The string is normally a sequence of decimal numbers separated
by periods, such as @samp{"2.6.0"}. The only reasonable use of this
macro is to incorporate it into a string constant.
@findex __CHAR_UNSIGNED__
This macro is defined if and only if the data type @code{char} is
unsigned on the target machine. It exists to cause the standard
-header file @file{limit.h} to work correctly. It is bad practice
+header file @file{limits.h} to work correctly. It is bad practice
to refer to this macro yourself; instead, refer to the standard
-macros defined in @file{limit.h}. The preprocessor uses
+macros defined in @file{limits.h}. The preprocessor uses
this macro to determine whether or not to sign-extend large character
constants written in octal; see @ref{#if Directive,,The @samp{#if} Directive}.
that don't together form a valid lexical unit cannot be concatenated. For
example, concatenation with @samp{x} on one side and @samp{+} on the other
is not meaningful because those two characters can't fit together in any
-lexical unit of C. The ANSI standard says that such attempts at
+lexical unit of C@. The ANSI standard says that such attempts at
concatenation are undefined, but in the GNU C preprocessor it is well
defined: it puts the @samp{x} and @samp{+} side by side with no particular
special results.
@noindent
provides the desired result.
-However, unintended grouping can result in another way. Consider
+Unintended grouping can result in another way. Consider
@samp{sizeof ceil_div(1, 2)}. That has the appearance of a C expression
that would compute the size of the type of @samp{ceil_div (1, 2)}, but in
fact it means something very different. Here is what it expands to:
corresponding @samp{#if}. Such comments should always be used, except in
short conditionals that are not nested. In fact, you can put anything at
all after the @samp{#endif} and it will be ignored by the GNU C preprocessor,
-but only comments are acceptable in ANSI Standard C.
+but only comments are acceptable in ANSI Standard C@.
@var{expression} is a C expression of integer type, subject to stringent
restrictions. It may contain
@findex #error
The directive @samp{#error} causes the preprocessor to report a fatal
error. The rest of the line that follows @samp{#error} is used as the
-error message.
+error message. The line must consist of complete tokens.
You would use @samp{#error} inside of a conditional that detects a
combination of parameters which you know the program does not properly
@smallexample
@group
#ifdef __vax__
-#error Won't work on Vaxen. See comments at get_last_object.
+#error "Won't work on Vaxen. See comments at get_last_object."
#endif
@end group
@end smallexample
some old C programs contain such lines.
@findex #pragma
-The ANSI standard specifies that the @samp{#pragma} directive has an
-arbitrary, implementation-defined effect. In the GNU C preprocessor,
+The ANSI standard specifies that the effect of the @samp{#pragma}
+directive is implementation-defined. In the GNU C preprocessor,
@samp{#pragma} directives are not used, except for @samp{#pragma once}
(@pxref{Once-Only}). However, they are left in the preprocessor output,
so they are available to the compilation pass.
This indicates that the following text comes from a system header file,
so certain warnings should be suppressed.
@item 4
-This indicates that the following text should be treated as C.
+This indicates that the following text should be treated as C@.
@c maybe cross reference NO_IMPLICIT_EXTERN_C
@end table
@item -traditional
@findex -traditional
-Try to imitate the behavior of old-fashioned C, as opposed to ANSI C.
+Try to imitate the behavior of old-fashioned C, as opposed to ANSI C@.
@itemize @bullet
@item
and @samp{4}.
@item
-A macro is not suppressed within its own definition, in traditional C.
+A macro is not suppressed within its own definition, in traditional C@.
Thus, any macro that is used recursively inevitably causes an error.
@item
The character @samp{#} has no special meaning within a macro definition
-in traditional C.
+in traditional C@.
@item
In traditional C, the text at the end of a macro expansion can run
together with the text after the macro call, to produce a single token.
-(This is impossible in ANSI C.)
+(This is impossible in ANSI C@.)
@item
Traditionally, @samp{\} inside a macro argument suppresses the syntactic
@item -Wall
@findex -Wall
Requests both @samp{-Wtrigraphs} and @samp{-Wcomment} (but not
-@samp{-Wtraditional}).
+@samp{-Wtraditional} or @samp{-Wundef}).
@item -Wtraditional
@findex -Wtraditional
Warn about certain constructs that behave differently in traditional and
-ANSI C.
+ANSI C@.
+
+@item -Wundef
+@findex -Wundef
+Warn if an undefined identifier is evaluated in an @samp{#if} directive.
@item -I @var{directory}
@findex -I
@findex -lang-objc++
Specify the source language. @samp{-lang-c} is the default; it
allows recognition of C++ comments (comments that begin with
-@samp{//} and end at end of line), since this is
-a common feature and it will most likely be in the next C standard.
-@samp{-lang-c89} disables recognition of C++ comments. @samp{-lang-c++}
+@samp{//} and end at end of line) and hexadecimal floating-point constants,
+since these features will most likely appear in the next C standard.
+@samp{-lang-c89} disables recognition of C++ comments and
+hexadecimal floating-point constants. @samp{-lang-c++}
handles C++ comment syntax and includes extra default include
directories for C++. @samp{-lang-objc} enables the Objective C
@samp{#import} directive. @samp{-lang-objc++} enables both C++ and Objective C
OSDN Git Service
