Packed

This is a simple header only C/C++ library that adds a more portable macro for defining a struct or enum as being packed, since most compilers have different ways of defining it.

Important Notes

As tempting as it might be, do not use packed structs/enums in public interfaces (ie. in libraries' public header files) since compilers don't agree on what packing means (hence why it is non-portable), you'll end up with issues where if someone uses the compiled version with a different compiler, things just won't work. As a result of this, you can use packed structs/enums within the precompiled part of a library, but you can't use them in the interface.

TL;DR: Don't use this is in a public interface for a library (ie. the installed header file(s)).

How to use this library

#include "packed.h"
// Or
#include <packed.h>

// Packed struct

packed_struct a {
    int a;
    char b;
    short c;
    int d;
};

// Non-packed struct
struct b {
    int a;
    char b;
    short c;
    int d;
};

// On GCC, sizeof(struct a) == 11, and sizeof(struct b) == 12 (at the time of writing this)

This is the same for C++, however, you'd use sizeof(a) instead of sizeof(struct a).

You only need to copy packed.h into your project, all other files aren't essential. (main.c and main.cpp are just used for testing).

This library is also compatible with the widely used typedef struct x {} x; pattern used in C, you just need to replace struct x {} in that example with packed_struct x {}.

Compiler Support

These compilers are known to work:

• Clang (tested 14.0.6)
• GCC (tested 12.2.0)
• MSVC (tested v19.33)
• TCC (tested 0.9.27)
• SDCC (tested 4.1.0) (No support for packed structs/enums)
• CC65 (tested 2.19) (No support for packed structs/enums)
• ICC (tested 2021.7.1)

If the compiler you use (idk, icc? - UPDATE: icc is basically GCC so it's supported) isn't listed on here then it currently isn't supported, however, feel free to submit a pull request updating packed.h to be able to support your compiler.

Notes on PRs that add support for other compilers

• When a compiler does not support packed structs/enums, then it's ok to create a PR that emits a warning message saying so (something along the lines of This compiler does not support packed structs/enums), I'd prefer this over a message stating that a compiler is not supported.
• Any detection method that can't be done in C preprocessor code (ie. your compiler does not have any predefined macros) won't be accepted, this is to keep the time for packed.h to be compiled at a minimum.