Function-Pointer in Interpreter

Question

I am building a C-Interpreter (in C++) which builds an AST. I want to give the user the opportunity to communicate with real DLLs. For example: I call a function from a DLL. This function expects an pointer to an function (to callback). There is the problem: I don't have a real address to a function, because the function which I want to give to the DLL-function only exists as node in my AST. Is there a way to solve the problem? I thought about using a proxy-like function built-in into my interpreter, which delegates to the function in my AST. The problem is, that the proxy-function must have the same signature to be callable from the DLL-function ... and i can't create dynamic functions at runtime.

Answer 1

You don't say specifically which API/dll you're trying to use, but MOST of them provide for a void * (or LPVOID on windows) of 'user data' that is supplied along with the callback function pointer and will be passed to the callback function, along with whatever other arguments are appropriate for the callback.

What you can do is pass in a pointer to your AST as this extra pointer, and write a small wrapper function for the actual callback which converts this void * back into an AST * and then invokes your interpreter on that AST.