what does #ifndef _WIN32 signify?

Question

Possible Duplicate:
the role of #ifdef and #ifndef

Does

#ifndef _WIN32

instruct the cpp to omit the code for 32 bit windows platform ?

Jay · Answer 1 · 2012-07-13T09:02:41.667

#ifndef _WIN32 tells the pre-processor to include the code below it till a corresponding #endif, if _WIN32 is not defined.

#ifndef _WIN32
#define STR1 "Some String"
#endif

The macro STR1 will get included if _WIN32 is not defined and will not get included if _WIN32 is defined. Please note that _WIN32 is a system defined macro. Generally, the code which is not meant for Windows platform or which is generic and cannot be compiled in Windows is placed under such #ifndef _WIN32 macros.

The MSDN page says _WIN32 will be defined by default for all 32 bit and 64 bit builds.

score 1 · Answer 2 · answered Jul 13 '12 at 08:51

1

This directive means "don't include this code when _WIN32 macro defined". If you define macro _WIN32 only when compile for the Win32 then this code "instruct the cpp to omit the code for 32 bit windows platform".

answered Jul 13 '12 at 08:51

Dmitry Poroh

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`_WIN32` will be defined by all compilers targeting Win32. You don't have to do that yourself. – Bo Persson Jul 13 '12 at 09:21
I'm not sure about "all compilers". – Dmitry Poroh Jul 13 '12 at 09:36

score 0 · Answer 3 · edited Jul 13 '12 at 12:48

Well it is a preprocessor directive. It is called compilation constants.

Compiler will consider the piece of code under those #ifndef if the compilation constant(such as, _WIN32) is not defined.

I believe above explanation will help you resolving your query.

To be more specific,

#ifndef _WIN32

...
...
...
some code
...
...
...

#endif

here if you have not defined _WIN32 (such as #define _WIN32) then the code within that #if...#endif will be compiled.

hope it helps.

what does #ifndef _WIN32 signify?

3 Answers3