@copying
@c man begin COPYRIGHT
Copyright @copyright{} 1987, 1989, 1991, 1992, 1993, 1994, 1995, 1996,
-1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
+1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007,
+2008, 2009, 2010
Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
-under the terms of the GNU Free Documentation License, Version 1.1 or
+under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation. A copy of
the license is included in the
@c man end
@ifinfo
@dircategory Software development
@direntry
-* Cpp: (cpp). The GNU C preprocessor.
+* Cpp: (cpp). The GNU C preprocessor.
@end direntry
@end ifinfo
@titlepage
@title The C Preprocessor
-@subtitle for GCC version @value{version-GCC}
-@author Richard M. Stallman
-@author Zachary Weinberg
+@versionsubtitle
+@author Richard M. Stallman, Zachary Weinberg
@page
@c There is a fill at the bottom of the page, so we need a filll to
@c override it.
* Include Operation::
* Search Path::
* Once-Only Headers::
+* Alternatives to Wrapper #ifndef::
* Computed Includes::
* Wrapper Headers::
* System Headers::
Obsolete Features
-* Assertions::
-* Obsolete once-only headers::
+* Obsolete Features::
@end detailmenu
@end menu
few things required by the standard. These are features which are
rarely, if ever, used, and may cause surprising changes to the meaning
of a program which does not expect them. To get strict ISO Standard C,
-you should use the @option{-std=c89} or @option{-std=c99} options, depending
+you should use the @option{-std=c90}, @option{-std=c99} or
+@option{-std=c1x} options, depending
on which version of the standard you want. To get all the mandatory
diagnostics, you must also use @option{-pedantic}. @xref{Invocation}.
* Include Operation::
* Search Path::
* Once-Only Headers::
+* Alternatives to Wrapper #ifndef::
* Computed Includes::
* Wrapper Headers::
* System Headers::
file, the macro name should contain the name of the file and some
additional text, to avoid conflicts with other header files.
+@node Alternatives to Wrapper #ifndef
+@section Alternatives to Wrapper #ifndef
+
+CPP supports two more ways of indicating that a header file should be
+read only once. Neither one is as portable as a wrapper @samp{#ifndef}
+and we recommend you do not use them in new programs, with the caveat
+that @samp{#import} is standard practice in Objective-C.
+
+@findex #import
+CPP supports a variant of @samp{#include} called @samp{#import} which
+includes a file, but does so at most once. If you use @samp{#import}
+instead of @samp{#include}, then you don't need the conditionals
+inside the header file to prevent multiple inclusion of the contents.
+@samp{#import} is standard in Objective-C, but is considered a
+deprecated extension in C and C++.
+
+@samp{#import} is not a well designed feature. It requires the users of
+a header file to know that it should only be included once. It is much
+better for the header file's implementor to write the file so that users
+don't need to know this. Using a wrapper @samp{#ifndef} accomplishes
+this goal.
+
+In the present implementation, a single use of @samp{#import} will
+prevent the file from ever being read again, by either @samp{#import} or
+@samp{#include}. You should not rely on this; do not use both
+@samp{#import} and @samp{#include} to refer to the same header file.
+
+Another way to prevent a header file from being included more than once
+is with the @samp{#pragma once} directive. If @samp{#pragma once} is
+seen when scanning a header file, that file will never be read again, no
+matter what.
+
+@samp{#pragma once} does not have the problems that @samp{#import} does,
+but it is not recognized by all preprocessors, so you cannot rely on it
+in a portable program.
+
@node Computed Includes
@section Computed Includes
@cindex computed includes
@item __OBJC__
This macro is defined, with value 1, when the Objective-C compiler is in
use. You can use @code{__OBJC__} to test whether a header is compiled
-by a C compiler or a Objective-C compiler.
+by a C compiler or an Objective-C compiler.
@item __ASSEMBLER__
This macro is defined with value 1 when preprocessing assembly
The common predefined macros are GNU C extensions. They are available
with the same meanings regardless of the machine or operating system on
-which you are using GNU C@. Their names all start with double
-underscores.
+which you are using GNU C or GNU Fortran. Their names all start with
+double underscores.
@table @code
+@item __COUNTER__
+This macro expands to sequential integral values starting from 0. In
+conjunction with the @code{##} operator, this provides a convenient means to
+generate unique identifiers. Care must be taken to ensure that
+@code{__COUNTER__} is not expanded prior to inclusion of precompiled headers
+which use it. Otherwise, the precompiled headers will not be used.
+
+@item __GFORTRAN__
+The GNU Fortran compiler defines this.
+
@item __GNUC__
@itemx __GNUC_MINOR__
@itemx __GNUC_PATCHLEVEL__
These macros are defined by all GNU compilers that use the C
-preprocessor: C, C++, and Objective-C@. Their values are the major
+preprocessor: C, C++, Objective-C and Fortran. Their values are the major
version, minor version, and patch level of the compiler, as integer
constants. For example, GCC 3.2.1 will define @code{__GNUC__} to 3,
@code{__GNUC_MINOR__} to 2, and @code{__GNUC_PATCHLEVEL__} to 1. These
This macro expands to a decimal integer constant that represents the
depth of nesting in include files. The value of this macro is
incremented on every @samp{#include} directive and decremented at the
-end of every included file. It starts out at 0, it's value within the
+end of every included file. It starts out at 0, its value within the
base file specified on the command line.
@item __ELF__
sure that programs will execute with the same effect whether or not they
are defined. If they are defined, their value is 1.
+@item __GNUC_GNU_INLINE__
+GCC defines this macro if functions declared @code{inline} will be
+handled in GCC's traditional gnu90 mode. Object files will contain
+externally visible definitions of all functions declared @code{inline}
+without @code{extern} or @code{static}. They will not contain any
+definitions of any functions declared @code{extern inline}.
+
+@item __GNUC_STDC_INLINE__
+GCC defines this macro if functions declared @code{inline} will be
+handled according to the ISO C99 standard. Object files will contain
+externally visible definitions of all functions declared @code{extern
+inline}. They will not contain definitions of any functions declared
+@code{inline} without @code{extern}.
+
+If this macro is defined, GCC supports the @code{gnu_inline} function
+attribute as a way to always get the gnu90 behavior. Support for
+this and @code{__GNUC_GNU_INLINE__} was added in GCC 4.1.3. If
+neither macro is defined, an older version of GCC is being used:
+@code{inline} functions will be compiled in gnu90 mode, and the
+@code{gnu_inline} function attribute will not be recognized.
+
@item __CHAR_UNSIGNED__
GCC defines this macro if and only if the data type @code{char} is
unsigned on the target machine. It exists to cause the standard header
@itemx __WINT_TYPE__
@itemx __INTMAX_TYPE__
@itemx __UINTMAX_TYPE__
+@itemx __SIG_ATOMIC_TYPE__
+@itemx __INT8_TYPE__
+@itemx __INT16_TYPE__
+@itemx __INT32_TYPE__
+@itemx __INT64_TYPE__
+@itemx __UINT8_TYPE__
+@itemx __UINT16_TYPE__
+@itemx __UINT32_TYPE__
+@itemx __UINT64_TYPE__
+@itemx __INT_LEAST8_TYPE__
+@itemx __INT_LEAST16_TYPE__
+@itemx __INT_LEAST32_TYPE__
+@itemx __INT_LEAST64_TYPE__
+@itemx __UINT_LEAST8_TYPE__
+@itemx __UINT_LEAST16_TYPE__
+@itemx __UINT_LEAST32_TYPE__
+@itemx __UINT_LEAST64_TYPE__
+@itemx __INT_FAST8_TYPE__
+@itemx __INT_FAST16_TYPE__
+@itemx __INT_FAST32_TYPE__
+@itemx __INT_FAST64_TYPE__
+@itemx __UINT_FAST8_TYPE__
+@itemx __UINT_FAST16_TYPE__
+@itemx __UINT_FAST32_TYPE__
+@itemx __UINT_FAST64_TYPE__
+@itemx __INTPTR_TYPE__
+@itemx __UINTPTR_TYPE__
These macros are defined to the correct underlying types for the
@code{size_t}, @code{ptrdiff_t}, @code{wchar_t}, @code{wint_t},
-@code{intmax_t}, and @code{uintmax_t}
-typedefs, respectively. They exist to make the standard header files
-@file{stddef.h} and @file{wchar.h} work correctly. You should not use
-these macros directly; instead, include the appropriate headers and use
-the typedefs.
+@code{intmax_t}, @code{uintmax_t}, @code{sig_atomic_t}, @code{int8_t},
+@code{int16_t}, @code{int32_t}, @code{int64_t}, @code{uint8_t},
+@code{uint16_t}, @code{uint32_t}, @code{uint64_t},
+@code{int_least8_t}, @code{int_least16_t}, @code{int_least32_t},
+@code{int_least64_t}, @code{uint_least8_t}, @code{uint_least16_t},
+@code{uint_least32_t}, @code{uint_least64_t}, @code{int_fast8_t},
+@code{int_fast16_t}, @code{int_fast32_t}, @code{int_fast64_t},
+@code{uint_fast8_t}, @code{uint_fast16_t}, @code{uint_fast32_t},
+@code{uint_fast64_t}, @code{intptr_t}, and @code{uintptr_t} typedefs,
+respectively. They exist to make the standard header files
+@file{stddef.h}, @file{stdint.h}, and @file{wchar.h} work correctly.
+You should not use these macros directly; instead, include the
+appropriate headers and use the typedefs. Some of these macros may
+not be defined on particular systems if GCC does not provide a
+@file{stdint.h} header on those systems.
@item __CHAR_BIT__
Defined to the number of bits used in the representation of the
@itemx __INT_MAX__
@itemx __LONG_MAX__
@itemx __LONG_LONG_MAX__
+@itemx __WINT_MAX__
+@itemx __SIZE_MAX__
+@itemx __PTRDIFF_MAX__
@itemx __INTMAX_MAX__
+@itemx __UINTMAX_MAX__
+@itemx __SIG_ATOMIC_MAX__
+@itemx __INT8_MAX__
+@itemx __INT16_MAX__
+@itemx __INT32_MAX__
+@itemx __INT64_MAX__
+@itemx __UINT8_MAX__
+@itemx __UINT16_MAX__
+@itemx __UINT32_MAX__
+@itemx __UINT64_MAX__
+@itemx __INT_LEAST8_MAX__
+@itemx __INT_LEAST16_MAX__
+@itemx __INT_LEAST32_MAX__
+@itemx __INT_LEAST64_MAX__
+@itemx __UINT_LEAST8_MAX__
+@itemx __UINT_LEAST16_MAX__
+@itemx __UINT_LEAST32_MAX__
+@itemx __UINT_LEAST64_MAX__
+@itemx __INT_FAST8_MAX__
+@itemx __INT_FAST16_MAX__
+@itemx __INT_FAST32_MAX__
+@itemx __INT_FAST64_MAX__
+@itemx __UINT_FAST8_MAX__
+@itemx __UINT_FAST16_MAX__
+@itemx __UINT_FAST32_MAX__
+@itemx __UINT_FAST64_MAX__
+@itemx __INTPTR_MAX__
+@itemx __UINTPTR_MAX__
+@itemx __WCHAR_MIN__
+@itemx __WINT_MIN__
+@itemx __SIG_ATOMIC_MIN__
Defined to the maximum value of the @code{signed char}, @code{wchar_t},
@code{signed short},
-@code{signed int}, @code{signed long}, @code{signed long long}, and
-@code{intmax_t} types
-respectively. They exist to make the standard header given numerical limits
-work correctly. You should not use these macros directly; instead, include
-the appropriate headers.
+@code{signed int}, @code{signed long}, @code{signed long long},
+@code{wint_t}, @code{size_t}, @code{ptrdiff_t},
+@code{intmax_t}, @code{uintmax_t}, @code{sig_atomic_t}, @code{int8_t},
+@code{int16_t}, @code{int32_t}, @code{int64_t}, @code{uint8_t},
+@code{uint16_t}, @code{uint32_t}, @code{uint64_t},
+@code{int_least8_t}, @code{int_least16_t}, @code{int_least32_t},
+@code{int_least64_t}, @code{uint_least8_t}, @code{uint_least16_t},
+@code{uint_least32_t}, @code{uint_least64_t}, @code{int_fast8_t},
+@code{int_fast16_t}, @code{int_fast32_t}, @code{int_fast64_t},
+@code{uint_fast8_t}, @code{uint_fast16_t}, @code{uint_fast32_t},
+@code{uint_fast64_t}, @code{intptr_t}, and @code{uintptr_t} types and
+to the minimum value of the @code{wchar_t}, @code{wint_t}, and
+@code{sig_atomic_t} types respectively. They exist to make the
+standard header given numerical limits work correctly. You should not
+use these macros directly; instead, include the appropriate headers.
+Some of these macros may not be defined on particular systems if GCC
+does not provide a @file{stdint.h} header on those systems.
+
+@item __INT8_C
+@itemx __INT16_C
+@itemx __INT32_C
+@itemx __INT64_C
+@itemx __UINT8_C
+@itemx __UINT16_C
+@itemx __UINT32_C
+@itemx __UINT64_C
+@itemx __INTMAX_C
+@itemx __UINTMAX_C
+Defined to implementations of the standard @file{stdint.h} macros with
+the same names without the leading @code{__}. They exist the make the
+implementation of that header work correctly. You should not use
+these macros directly; instead, include the appropriate headers. Some
+of these macros may not be defined on particular systems if GCC does
+not provide a @file{stdint.h} header on those systems.
+
+@item __SIZEOF_INT__
+@itemx __SIZEOF_LONG__
+@itemx __SIZEOF_LONG_LONG__
+@itemx __SIZEOF_SHORT__
+@itemx __SIZEOF_POINTER__
+@itemx __SIZEOF_FLOAT__
+@itemx __SIZEOF_DOUBLE__
+@itemx __SIZEOF_LONG_DOUBLE__
+@itemx __SIZEOF_SIZE_T__
+@itemx __SIZEOF_WCHAR_T__
+@itemx __SIZEOF_WINT_T__
+@itemx __SIZEOF_PTRDIFF_T__
+Defined to the number of bytes of the C standard data types: @code{int},
+@code{long}, @code{long long}, @code{short}, @code{void *}, @code{float},
+@code{double}, @code{long double}, @code{size_t}, @code{wchar_t}, @code{wint_t}
+and @code{ptrdiff_t}.
+
+@item __BYTE_ORDER__
+@itemx __ORDER_LITTLE_ENDIAN__
+@itemx __ORDER_BIG_ENDIAN__
+@itemx __ORDER_PDP_ENDIAN__
+@code{__BYTE_ORDER__} is defined to one of the values
+@code{__ORDER_LITTLE_ENDIAN__}, @code{__ORDER_BIG_ENDIAN__}, or
+@code{__ORDER_PDP_ENDIAN__} to reflect the layout of multi-byte and
+multi-word quantities in memory. If @code{__BYTE_ORDER__} is equal to
+@code{__ORDER_LITTLE_ENDIAN__} or @code{__ORDER_BIG_ENDIAN__}, then
+multi-byte and multi-word quantities are laid out identically: the
+byte (word) at the lowest address is the least significant or most
+significant byte (word) of the quantity, respectively. If
+@code{__BYTE_ORDER__} is equal to @code{__ORDER_PDP_ENDIAN__}, then
+bytes in 16-bit words are laid out in a little-endian fashion, whereas
+the 16-bit subwords of a 32-bit quantity are laid out in big-endian
+fashion.
+
+You should use these macros for testing like this:
+
+@smallexample
+/* @r{Test for a little-endian machine} */
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+@end smallexample
+
+@item __FLOAT_WORD_ORDER__
+@code{__FLOAT_WORD_ORDER__} is defined to one of the values
+@code{__ORDER_LITTLE_ENDIAN__} or @code{__ORDER_BIG_ENDIAN__} to reflect
+the layout of the words of multi-word floating-point quantities.
@item __DEPRECATED
This macro is defined, with value 1, when compiling a C++ source file
@item __EXCEPTIONS
This macro is defined, with value 1, when compiling a C++ source file
-with exceptions enabled. If @option{-fno-exceptions} was used when
-compiling the file, then this macro will not be defined.
+with exceptions enabled. If @option{-fno-exceptions} is used when
+compiling the file, then this macro is not defined.
+
+@item __GXX_RTTI
+This macro is defined, with value 1, when compiling a C++ source file
+with runtime type identification enabled. If @option{-fno-rtti} is
+used when compiling the file, then this macro is not defined.
@item __USING_SJLJ_EXCEPTIONS__
This macro is defined, with value 1, if the compiler uses the old
(once per compilation) and @code{__TIMESTAMP__} will expand to
@code{@w{"??? ??? ?? ??:??:?? ????"}}.
+@item __GCC_HAVE_SYNC_COMPARE_AND_SWAP_1
+@itemx __GCC_HAVE_SYNC_COMPARE_AND_SWAP_2
+@itemx __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4
+@itemx __GCC_HAVE_SYNC_COMPARE_AND_SWAP_8
+@itemx __GCC_HAVE_SYNC_COMPARE_AND_SWAP_16
+These macros are defined when the target processor supports atomic compare
+and swap operations on operands 1, 2, 4, 8 or 16 bytes in length, respectively.
+
+@item __GCC_HAVE_DWARF2_CFI_ASM
+This macro is defined when the compiler is emitting Dwarf2 CFI directives
+to the assembler. When this is defined, it is possible to emit those same
+directives in inline assembly.
+
+@item __FP_FAST_FMA
+@itemx __FP_FAST_FMAF
+@itemx __FP_FAST_FMAL
+These macros are defined with value 1 if the backend supports the
+@code{fma}, @code{fmaf}, and @code{fmal} builtin functions, so that
+the include file @file{math.h} can define the macros
+@code{FP_FAST_FMA}, @code{FP_FAST_FMAF}, and @code{FP_FAST_FMAL}
+for compatibility with the 1999 C standard.
@end table
@node System-specific Predefined Macros
preprocessor itself. Other pragmas are meaningful to the C or C++
compilers. They are documented in the GCC manual.
+GCC plugins may provide their own pragmas.
+
@ftable @code
@item #pragma GCC dependency
@code{#pragma GCC dependency} allows you to check the relative dates of
@item The mapping of physical source file multi-byte characters to the
execution character set.
-Currently, CPP requires its input to be ASCII or UTF-8. The execution
-character set may be controlled by the user, with the
-@option{-fexec-charset} and @option{-fwide-exec-charset} options.
+The input character set can be specified using the
+@option{-finput-charset} option, while the execution character set may
+be controlled using the @option{-fexec-charset} and
+@option{-fwide-exec-charset} options.
@item Identifier characters.
@anchor{Identifier characters}
identifier characters by default.
Currently the targets that by default do not permit @samp{$} are AVR,
-IP2K, MMIX, MIPS Irix 3, ARM aout, and PowerPC targets for the AIX and
-BeOS operating systems.
+IP2K, MMIX, MIPS Irix 3, ARM aout, and PowerPC targets for the AIX
+operating system.
You can override the default with @option{-fdollars-in-identifiers} or
@option{fno-dollars-in-identifiers}. @xref{fdollars-in-identifiers}.
same way; i.e.@: escape sequences such as @samp{\a} are given the
values they would have on the target machine.
-The compiler values a multi-character character constant a character
+The compiler evaluates a multi-character character constant a character
at a time, shifting the previous value left by the number of bits per
target character, and then or-ing in the bit-pattern of the new
character truncated to the width of a target character. The final
@node Obsolete Features
@section Obsolete Features
-CPP has a number of features which are present mainly for
-compatibility with older programs. We discourage their use in new code.
-In some cases, we plan to remove the feature in a future version of GCC@.
+CPP has some features which are present mainly for compatibility with
+older programs. We discourage their use in new code. In some cases,
+we plan to remove the feature in a future version of GCC@.
-@menu
-* Assertions::
-* Obsolete once-only headers::
-@end menu
-
-@node Assertions
@subsection Assertions
@cindex assertions
You can also make or cancel assertions using command line options.
@xref{Invocation}.
-@node Obsolete once-only headers
-@subsection Obsolete once-only headers
-
-CPP supports two more ways of indicating that a header file should be
-read only once. Neither one is as portable as a wrapper @samp{#ifndef},
-and we recommend you do not use them in new programs.
-
-@findex #import
-In the Objective-C language, there is a variant of @samp{#include}
-called @samp{#import} which includes a file, but does so at most once.
-If you use @samp{#import} instead of @samp{#include}, then you don't
-need the conditionals inside the header file to prevent multiple
-inclusion of the contents. GCC permits the use of @samp{#import} in C
-and C++ as well as Objective-C@. However, it is not in standard C or C++
-and should therefore not be used by portable programs.
-
-@samp{#import} is not a well designed feature. It requires the users of
-a header file to know that it should only be included once. It is much
-better for the header file's implementor to write the file so that users
-don't need to know this. Using a wrapper @samp{#ifndef} accomplishes
-this goal.
-
-In the present implementation, a single use of @samp{#import} will
-prevent the file from ever being read again, by either @samp{#import} or
-@samp{#include}. You should not rely on this; do not use both
-@samp{#import} and @samp{#include} to refer to the same header file.
-
-Another way to prevent a header file from being included more than once
-is with the @samp{#pragma once} directive. If @samp{#pragma once} is
-seen when scanning a header file, that file will never be read again, no
-matter what.
-
-@samp{#pragma once} does not have the problems that @samp{#import} does,
-but it is not recognized by all preprocessors, so you cannot rely on it
-in a portable program.
-
@node Differences from previous versions
@section Differences from previous versions
@cindex differences from previous versions
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