Can I Safely Store and Retrieve C Structs Across Different Platforms and Compilers?

Can I Safely Read/Write Cross-Platform/Compiler-Compatible Structs to Files?

Structs in C present a challenge for cross-platform compatibility due to potential differences in padding between compilers. This disparity arises from the lack of standardization in C at the binary level.

As Don Box explains in his book, "Essential COM," C 's binary runtime model is not standardized. Therefore, different compilers can employ varying padding alignments for structs, even when using the same compiler with different pragma pack directives.

Furthermore, the order of member declaration within a struct can affect its size, even if the members remain identical. For example:

struct A {
    char c;
    char d;
    int i;
};

struct B {
    char c;
    int i;
    char d;
};

Compiled with gcc-4.3.4, the sizes of A and B differ despite their identical members:

Size of A: 8
Size of B: 12

This disparity makes it impossible to assume that all compilers will pad structs in the same way. Therefore, there is no guaranteed method for safely reading/writing structs to files in a cross-platform/compiler-compatible manner.

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