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Asked: 2026-05-11T05:57:47+00:00

I was looking through some code from the SDL library and came across a

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I was looking through some code from the SDL library and came across a function declared like this:

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)

Now, I’m a Delphi coder. No hablo C muy bien, senor. But I remember enough syntax from my college courses to read it like this:

Function name is WndProc. Argument list is pretty self-explanatory. Function return type is LRESULT. But what in the world is that ‘CALLBACK’ doing there? In Delphi, any function can be used as a callback; you just need to pass the right type of function pointer. Is there any particular reason why C doesn’t work that way? Or does it mean something different?

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  1. The "CALLBACK" is a calling convention. There are other kinds of calling conventions. CALLBACK is the same as __stdcall.

    http://www.codeguru.com/cpp/cpp/cpp_mfc/callbacks/article.php/c10557

    Some more information at Raymond Chen’s blog:

    https://devblogs.microsoft.com/oldnewthing/20040108-00/?p=41163

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