Strange function call coding

This is in C++. Im looking through code. Part of it has the following

void __stdcall function1(int param1, Byte param2, void* param3)
{
//function code
}

then when its called its as a parameter to another function


Result = function2(param1, function1, (void *) param3);

Function1 is being called with no parameters. There is no default values set for these parameters so can anyone explain to me whats goin on here?

Cheers