Guide to predefined macros in C++ compilers (gcc, clang, msvc etc.)

https://blog.kowalczyk.info/article/j/guide-to-predefined-macros-in-c-compilers-gcc-clang-msvc-etc..html

When writing portable C++ code you need to write conditional code that depends on compiler used or the OS for which the code is written. To perform those checks you need to check pre-processor macros that various compilers set.

To list gcc’s pre-defined macros: gcc -x c /dev/null -dM -E

The -x c /dev/null -dM -E also works for mingw (which is based on gcc). tdm-gcc不好使，把 /dev/null 换成 nul: 可以。

Option Summary (Using the GNU Compiler Collection (GCC))

• -x language Specify explicitly the language for the following input files (rather than letting the compiler choose a default based on the file name suffix).
• -dM Instead of the normal output, generate a list of ‘#define’ directives for all the macros defined during the execution of the preprocessor, including predefined macros.
• -E Stop after the preprocessing stage; do not run the compiler proper.

...
#define __MINGW32__ 1
#define __GNUC__ 10
#define __VERSION__ "10.3.0"
#define WINNT 1
#define WIN32 1 // ifdef WIN32和ifdef _WIN32都能用没啥神秘的，因为两个都定义了。按字符算钱的话，还有__WIN32__ 
#define _WIN32 1
#define __WINNT 1
#define __WINNT__ 1
#define __WIN32__ 1
...
#define __WCHAR_WIDTH__ 16
#define __WCHAR_MAX__ 0xffff
...
#define __declspec(x) __attribute__((x))
...
#define __INT64_C(c) c ## LL
#define __UINT64_C(c) c ## ULL