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 cpp (C preprocessor).

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How to see macros expansion?

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GCC::

  $ cpp <file>.c

MSVC::

  $ cl /E <file>.c

Under Emacs select region and type ``C-c C-e``.

How to see predefined macros?

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See:

  http://predef.sourceforge.net/

                ``predef`` project on Sourceforge

  http://en.wikipedia.org/wiki/C_preprocessor#Compiler-specific_predefined_macros

                Compiler specific predefined macros

  http://msdn.microsoft.com/en-us/library/b0084kay.aspx

                Predefined Macros

GNU C Compiler::

  $ gcc -dM -E - < /dev/null

HP-UX ansi C compiler::

  $ cc -v EMPTY.c

SCO OpenServer C compiler::

  $ cc -## EMPTY.c

Sun Studio C/C++ compiler::

  $ cc -## EMPTY.c

IBM AIX XL C/C++ compiler::

  $ cc -qshowmacros -E EMPTY.c

For Visual Studio compiler there no any possibility get predefined macros from

command line... But some macros documented:

  _MSC_VER

                Defines the compiler version. Always defined.

  _WIN32

                Defined for applications for Win32. Always defined.