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Asked: 2026-05-11T12:40:22+00:00

In an application I maintain, we’ve encountered a problem with file descriptor limitations affecting

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In an application I maintain, we’ve encountered a problem with file descriptor limitations affecting the stdlib. This problem only affects the 32-bit version of the standard lib.

I have devised a fix for my code and would like to implement it, but only when compiling for 32-bit executable. What pre-processor symbol can I #ifdef for to determine whether the code is being compiled for a 32 or 64-bit target?

EDIT

Sorry, didn’t mention, the code is cross-platform, linux, windows, solaris and a few other unix flavors, mostly using GCC for compilation. Any de-facto standards I can use cross-platform?

EDIT 2

I’ve found some definitions ‘__ILP23’ and ‘__LP64’ that seem like they may work… a discussion here explains the background on the unix platform. Anyone had any experience with using these defines? Is this going to be usable?

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1 Answer

  1. I’m not sure if there is a universal #if def that is appropriate. The C++ standard almost certainly does not define one. There are certainly platform spcefic ones though.

    For example, Windows

    #if _WIN64  // 64 bit build #else // 32 bit build #endif

    EDIT OP mentioned this is a cross compile between Windows and Non-Windows using GCC and other compilers

    There is no universal macro that can be used for all platforms and compilers. A little bit of preprocessor magic though can do the trick. Assuming you’re only working on x86 and amd64 chips the following should do the trick. It can easily be expanded for other platforms though

    #if _WIN64 || __amd64__ #define PORTABLE_64_BIT #else #define PORTABLE_32_BIT #endif
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