Calling conventions

There’re several conventions of calling functions, specifying who (caller or callee) pops arguments from the stack, how arguments are passed and in what order. C++ uses Cdecl calling convention by default, but C# expects StdCall, which is usually used by Windows API. You need to change one or the other:

• Change calling convention to StdCall in C++:

extern "C" __declspec(dllexport) int __stdcall add(int a, int b)

[DllImport("myDLL.dll")]

• Or, change calling convention to Cdecl in C#:

extern "C" __declspec(dllexport) int /*__cdecl*/ add(int a, int b)

[DllImport("myDLL.dll", CallingConvention = CallingConvention.Cdecl)]

If you want to use a function with Cdecl calling convention and a mangled name, your code will look like this:

__declspec(dllexport) int add(int a, int b)

[DllImport("myDLL.dll", CallingConvention = CallingConvention.Cdecl,
           EntryPoint = "?add@@YAHHH@Z")]

• thiscall(**__thiscall**) is mainly used in functions that are members of a class.
• When a function uses thiscall(**__thiscall**) , a pointer to the class is passed down as the first parameter.