How to know if 32 or 64 linux.

[ChrisW67]

Assuming you are are using GCC on Linux then these predefined macros may be useful:

__i386__	You're compiling for a 32-bit Intel
__x86_64__	You're compiling for a 64-bit Intel
__ppc__	You're compiling for a 32-bit PowerPC
__ppc64__	You're compiling for a 64-bit PowerPC
 
__LP64__  possibly an indicator of 64-bitness

__i386__	You're compiling for a 32-bit Intel
__x86_64__	You're compiling for a 64-bit Intel
__ppc__	You're compiling for a 32-bit PowerPC
__ppc64__	You're compiling for a 64-bit PowerPC

__LP64__  possibly an indicator of 64-bitness

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You can see what your GCC defines with:

cpp -dM -E < /dev/null

cpp -dM -E < /dev/null

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You could also peruse qglobal.h for hints as to how the Qt system does it.

http://predef.sourceforge.net/ is also very useful