👀 Views: 69 💬 Answers: 1 📅 Created: 2025-06-11

c function-pointers calling-conventions C

I've been struggling with this for a few days now and could really use some help. I've been banging my head against this for hours. I'm encountering a perplexing issue with function pointers in a struct when using different calling conventions in C. I've defined a struct that contains a function pointer, and depending on how I call the function, it seems to result in an inconsistent behavior, especially when mixing `__cdecl` and `__stdcall` conventions. Here’s a simplified version of my code: ```c #include <stdio.h> // Function declaration with cdecl void __cdecl myFunction(int x) { printf("Value: %d\n", x); } // Function declaration with stdcall void __stdcall anotherFunction(int x) { printf("Value from stdcall: %d\n", x); } typedef struct { void (*func)(int); } FuncHolder; int main() { FuncHolder holder; holder.func = myFunction; // Assigning cdecl function holder.func(10); // Works fine holder.func = anotherFunction; // Assigning stdcall function holder.func(20); // Causes unexpected behavior return 0; } ``` When I run this code, the first function call works perfectly, but when I try to call `anotherFunction`, the program crashes. I'm compiling this with GCC 10.2 on Windows and using the default calling convention. I tried using `__declspec(naked)` for the `anotherFunction`, thinking it might help, but it didn't resolve the crashing issue. I've also read about mixing calling conventions potentially causing stack issues, but I'm not sure how to properly handle this scenario. Is there a best practice or a workaround to safely use different calling conventions with function pointers in structs? How can I ensure that my struct remains flexible without running into these complications? Any insights would be greatly appreciated! Am I missing something obvious? This is my first time working with C 3.10. Could this be a known issue? I'm working on a service that needs to handle this. I'd love to hear your thoughts on this.