I'm trying to call a function with a function pointer in C++, but I can't find any convention that fits it. Its stack arguments are (right to left):

func(float x, float y, int unk);

...but ecx needs to be pointing to a buffer it can use for output / storage. That would be __thiscall, but the caller cleans up the stack (adds 12 to esp). This is what I have right now:

((void(__thiscall*)(char*,float,float,int))(0x1234567))(a, b, c);

but it causes the application to crash because the stack isn't evened.

How can I call this?

  • that sounds more like a fastcall, if ecx points to an integer store May 11, 2016 at 16:02
  • are you sure ecx is used to pass the buffer and not the class instance? please post a fragment of assembly.
    – Igor Skochinsky
    May 24, 2017 at 0:26

1 Answer 1


Sounds like you have a variadic __thiscall function (printf-like). Those use ecx for this but the remaining arguments are pushed onto the stack and the caller cleans it up.

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