C preprocessor

lastmod 2025-02-13created 2016-04-1915 edits

A macro is a keyword that tells the compiler about characteristics of the code. It is therefore an element needed in the process of compiling to machine code; the macro itself does not generate machine code, but it is used to control specific code.

List of C/C++ preprocessor

MSVC
MWCC
BCC
EDG
DMC

Built-in macros

__DATE__: Replaced with the compile date as a string.
__TIME__: Replaced with the compile time as a string.
__LINE__: Replaced with the line number being compiled as an integer.
__FILE__: Replaced with the name of the file currently being compiled as a string.
__TIMESTAMP__: Replaced with the last modification date and time of the source file as a string.
__VA_ARGS__: Stands in for variadic arguments (...).
__cplusplus: determines if your compiler is in C or C++ mode. Usually used in headers
__PRETTY_FUNCTION__: Returns the class name and function name containing the source code in a pretty format.

About variadic macros

http://kldp.org/node/68888

#define TRACE(fmt, ...) printf(fmt, __VA_ARGS__)

Rather than the above,

#define TRACE(...) printf(__VA_ARGS__)

is better. Because when you write TRACE("hello"), the former expands as follows and becomes a syntax error:

printf("hello", )

Visual C++ Preprocessor Reference

http://msdn.microsoft.com/ko-kr/library/dtefa218

Describes the preprocessor as it is implemented in Microsoft C and C++.

Preprocessor Directives	#define Directive, #error Directive, #import Directive, #include Directive, #line Directive, #undef Directive, #using Directive, Null Directive
Preprocessor Directives (Condition check)	#if, #elif, #else, and #endif Directives, #ifdef and #ifndef Directives
Preprocessor Operators	Stringizing Operator (#), Charizing Operator (#@), Token-Pasting Operator (##)
Predefined Macros	Macros and C++, Variadic Macros, Predefined Macros
Pragmas

Print message

Is there a portable way to print a message from the C preprocessor?

The warning directive is probably the closest you'll get, but it's not entirely platform-independent:

#warning "C Preprocessor got here!"

AFAIK this works on most compilers except MSVC, on which you'll have to use a pragma directive:

#pragma message ( "C Preprocessor got here!" )

Print error message

#ifndef NPY_DEPRECATED_INCLUDES
#error "Should never include npy_*_*_deprecated_api directly."
#endif

Print warning message

#if defined(_WIN32)
#define _WARN___STR2__(x) #x
#define _WARN___STR1__(x) _WARN___STR2__(x)
#define _WARN___LOC__ __FILE__ "("_WARN___STR1__(__LINE__)") : Warning Msg: "
#pragma message(_WARN___LOC__"Using deprecated NumPy API, disable it by " \
                         "#defining NPY_NO_DEPRECATED_API NPY_1_7_API_VERSION")
#elif defined(__GNUC__)
#warning "Using deprecated NumPy API, disable it by " \
         "#defining NPY_NO_DEPRECATED_API NPY_1_7_API_VERSION"
#endif

Pre-defined Compiler Macros

Stackoverflow: How do I check OS with a preprocessor directive?
Pre-defined Compiler Macros
[https://blog.kowalczyk.info/article/j/guide-to-predefined-macros-in-c-compilers-gcc-clang-msvc-etc..html Guide to predefined macros in C++ compilers (gcc, clang, msvc etc.)]

Windows

Taken from the Visual C docs, the most common ones are:

_WIN32: Both 32 bit and 64 bit
_WIN64: 64 bit only

MSVC

Unix (Linux, *BSD, Mac OS X)

unix
__unix
__unix__

GCC

GCC - C++ Standards Support in GCC

Mac OS X

__APPLE__
__MACH__

Linux

The Linux GCC HOWTO
__linux__

FreeBSD

Differentiating Operating Systems and OS Versions
__FreeBSD__

CLANG

Preprocessor checker

The Boost:Preprocessor code contains code for checking the preprocessor. (/boost/preprocessor/config/config.hpp)

# /* **************************************************************************
#  *                                                                          *
#  *     (C) Copyright Paul Mensonides 2002-2011.                             *
#  *     (C) Copyright Edward Diener 2011.                                    *
#  *     Distributed under the Boost Software License, Version 1.0. (See      *
#  *     accompanying file LICENSE_1_0.txt or copy at                         *
#  *     http://www.boost.org/LICENSE_1_0.txt)                                *
#  *                                                                          *
#  ************************************************************************** */
#
# /* See http://www.boost.org for most recent version. */
#
# ifndef BOOST_PREPROCESSOR_CONFIG_CONFIG_HPP
# define BOOST_PREPROCESSOR_CONFIG_CONFIG_HPP
#
# /* BOOST_PP_CONFIG_FLAGS */
#
# define BOOST_PP_CONFIG_STRICT() 0x0001
# define BOOST_PP_CONFIG_IDEAL() 0x0002
#
# define BOOST_PP_CONFIG_MSVC() 0x0004
# define BOOST_PP_CONFIG_MWCC() 0x0008
# define BOOST_PP_CONFIG_BCC() 0x0010
# define BOOST_PP_CONFIG_EDG() 0x0020
# define BOOST_PP_CONFIG_DMC() 0x0040
#
# ifndef BOOST_PP_CONFIG_FLAGS
#    if defined(__GCCXML__)
#        define BOOST_PP_CONFIG_FLAGS() (BOOST_PP_CONFIG_STRICT())
#    elif defined(__WAVE__)
#        define BOOST_PP_CONFIG_FLAGS() (BOOST_PP_CONFIG_STRICT())
#    elif defined(__MWERKS__) && __MWERKS__ >= 0x3200
#        define BOOST_PP_CONFIG_FLAGS() (BOOST_PP_CONFIG_STRICT())
#    elif defined(__EDG__) || defined(__EDG_VERSION__)
#        if defined(_MSC_VER) && (defined(__INTELLISENSE__) || __EDG_VERSION__ >= 308)
#            define BOOST_PP_CONFIG_FLAGS() (BOOST_PP_CONFIG_MSVC())
#        else
#            define BOOST_PP_CONFIG_FLAGS() (BOOST_PP_CONFIG_EDG() | BOOST_PP_CONFIG_STRICT())
#        endif
#    elif defined(__MWERKS__)
#        define BOOST_PP_CONFIG_FLAGS() (BOOST_PP_CONFIG_MWCC())
#    elif defined(__DMC__)
#        define BOOST_PP_CONFIG_FLAGS() (BOOST_PP_CONFIG_DMC())
#    elif defined(__BORLANDC__) && __BORLANDC__ >= 0x581
#        define BOOST_PP_CONFIG_FLAGS() (BOOST_PP_CONFIG_STRICT())
#    elif defined(__BORLANDC__) || defined(__IBMC__) || defined(__IBMCPP__) || defined(__SUNPRO_CC)
#        define BOOST_PP_CONFIG_FLAGS() (BOOST_PP_CONFIG_BCC())
#    elif defined(_MSC_VER) && !defined(__clang__)
#        define BOOST_PP_CONFIG_FLAGS() (BOOST_PP_CONFIG_MSVC())
#    else
#        define BOOST_PP_CONFIG_FLAGS() (BOOST_PP_CONFIG_STRICT())
#    endif
# endif
#
# /* BOOST_PP_CONFIG_EXTENDED_LINE_INFO */
#
# ifndef BOOST_PP_CONFIG_EXTENDED_LINE_INFO
#    define BOOST_PP_CONFIG_EXTENDED_LINE_INFO 0
# endif
#
# /* BOOST_PP_CONFIG_ERRORS */
#
# ifndef BOOST_PP_CONFIG_ERRORS
#    ifdef NDEBUG
#        define BOOST_PP_CONFIG_ERRORS 0
#    else
#        define BOOST_PP_CONFIG_ERRORS 1
#    endif
# endif
#
# /* BOOST_PP_VARIADICS */
#
# define BOOST_PP_VARIADICS_MSVC 0
# if !defined BOOST_PP_VARIADICS
#    /* variadic support explicitly disabled for all untested compilers */
#    if defined __GCCXML__ || defined __CUDACC__ || defined __PATHSCALE__ || defined __DMC__ || defined __CODEGEARC__ || defined __BORLANDC__ || defined __MWERKS__ || ( defined __SUNPRO_CC && __SUNPRO_CC < 0x5130 ) || defined __HP_aCC && !defined __EDG__ || defined __MRC__ || defined __SC__ || defined __IBMCPP__ || defined __PGI
#        define BOOST_PP_VARIADICS 0
#    /* VC++ (C/C++) */
#    elif defined _MSC_VER && _MSC_VER >= 1400 && (!defined __EDG__ || defined(__INTELLISENSE__)) && !defined __clang__
#        define BOOST_PP_VARIADICS 1
#        undef BOOST_PP_VARIADICS_MSVC
#        define BOOST_PP_VARIADICS_MSVC 1
#    /* Wave (C/C++), GCC (C++) */
#    elif defined __WAVE__ && __WAVE_HAS_VARIADICS__ || defined __GNUC__ && defined __GXX_EXPERIMENTAL_CXX0X__ && __GXX_EXPERIMENTAL_CXX0X__
#        define BOOST_PP_VARIADICS 1
#    /* EDG-based (C/C++), GCC (C), and unknown (C/C++) */
#    elif !defined __cplusplus && __STDC_VERSION__ >= 199901L || __cplusplus >= 201103L
#        define BOOST_PP_VARIADICS 1
#    else
#        define BOOST_PP_VARIADICS 0
#    endif
# elif !BOOST_PP_VARIADICS + 1 < 2
#    undef BOOST_PP_VARIADICS
#    define BOOST_PP_VARIADICS 1
#    if defined _MSC_VER && _MSC_VER >= 1400 && (defined(__INTELLISENSE__) || !(defined __EDG__ || defined __GCCXML__ || defined __CUDACC__ || defined __PATHSCALE__ || defined __clang__ || defined __DMC__ || defined __CODEGEARC__ || defined __BORLANDC__ || defined __MWERKS__ || defined __SUNPRO_CC || defined __HP_aCC || defined __MRC__ || defined __SC__ || defined __IBMCPP__ || defined __PGI))
#        undef BOOST_PP_VARIADICS_MSVC
#        define BOOST_PP_VARIADICS_MSVC 1
#    endif
# else
#    undef BOOST_PP_VARIADICS
#    define BOOST_PP_VARIADICS 0
# endif
#
# endif

A simpler version:

#if defined(WIN32) || defined(_WIN32) || defined(__WIN32__) || defined(__NT__)
   //define something for Windows (32-bit and 64-bit, this part is common)
   #ifdef _WIN64
      //define something for Windows (64-bit only)
   #else
      //define something for Windows (32-bit only)
   #endif
#elif __APPLE__
    #include <TargetConditionals.h>
    #if TARGET_IPHONE_SIMULATOR
         // iOS, tvOS, or watchOS Simulator
    #elif TARGET_OS_MACCATALYST
         // Mac's Catalyst (ports iOS API into Mac, like UIKit).
    #elif TARGET_OS_IPHONE
        // iOS, tvOS, or watchOS device
    #elif TARGET_OS_MAC
        // Other kinds of Apple platforms
    #else
    #   error "Unknown Apple platform"
    #endif
#elif __ANDROID__
    // Below __linux__ check should be enough to handle Android,
    // but something may be unique to Android.
#elif __linux__
    // linux
#elif __unix__ // all unices not caught above
    // Unix
#elif defined(_POSIX_VERSION)
    // POSIX
#else
#   error "Unknown compiler"
#endif

Favorite site

Documentation

The C Preprocessor: Macros
- 3.3 Macro Arguments
- [Recommended] 3.10.6 Argument Prescan

Tip & Trick

KLDP: Using the preprocessor #define do{ statement1; statement2; statement3 }while(0)
[Recommended] Stackoverflow - Can we have recursive macros? (Issues with recursive use of macros)
Detect empty macro arguments
pragma - once, pack, warning, comment, link ²
Preprocessor directives - #include, #define, #undef, #if, #else, #endif, #ifdef, #elif, #ifndef, defined(), #error, #line ³

References

The_type_of_c_preprocessor.pdf ↩
Pragma-once_pack_warning_comment_link.pdf ↩
Preprocessor-include_define_undef_if_else_endif_ifdef_elif_ifndef_defined_error_line.pdf ↩

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