Detecting Structure Padding

This is a discussion on Detecting Structure Padding within the C++ Programming forums, part of the General Programming Boards category; I'm creating a header file (to be included in DLL projects) that allows DLLs to communicate with the larger, main ...

  1. #1
    Registered User johnnie2's Avatar
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    Detecting Structure Padding

    I'm creating a header file (to be included in DLL projects) that allows DLLs to communicate with the larger, main application. The header file declares a struct, and I've figured that the structure must be packed to ensure that different compilers don't insert padding in different places, leading to a situation in which the application and the DLLs (built with different compilers) have separate views of the same struct definition.

    However, different compilers have varying ways of indicating that a structure should be packed (VC++'s pragma directive as opposed to MingW's __attribute__); is there a way to detect which compiler is being used so the correct directive may be invoked?
    "Optimal decisions, once made, do not need to be changed." - Robert Sedgewick, Algorithms in C

  2. #2
    Registered User Codeplug's Avatar
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    For VC++ it is
    Code:
    #ifdef _MSC_VER
    //Microsoft compiler
    #endif
    For gnu c/c++ it is
    Code:
    #ifdef __GNUC__
    //GNU compiler
    #endif
    gg

  3. #3
    Registered User johnnie2's Avatar
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    Thanks. The information I found is as follows:

    Microsoft VC++
    _MSC_VER
    #pragma pack(1) / #pragma pack(pop)

    Borland C++
    _BORLANDC_
    #pragma pack(1) / #pragma pack()

    GNU C++
    __GNUC__
    __attribute__((packed))
    "Optimal decisions, once made, do not need to be changed." - Robert Sedgewick, Algorithms in C

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