How to make a callback global so I can use it to other functions?

Question

I declared a function like this:

int __stdcall DoSomething(int &inputSize, int &outputSize, void(* __stdcall progress)(int) )
{
}

How can I make progress() callback a global variable to use it in other functions in the same DLL? I am a newbie to C++.

@deviantfan But this another function should declare progress argument the same way? void(* __stdcall progress)(int) ? — Tom, Oct 09 '15 at 20:40
Also consider using a `typedef` for the function pointer type. That makes things look nicer, especially when various functions take it as a parameter. (And makes things easier if you ever need to modify the callback's signature.) — TheUndeadFish, Oct 09 '15 at 21:17

James Adkison · Accepted Answer · 2015-10-09T20:53:22.273

Create a function with a matching signature (i.e., void (*)(int)).

#include <iostream>

//void (      *      )(     int    ) - same signature as the function callback
  void progressHandler(int progress)
{
    std::cout << "received progress: " << progress << std::endl;
}

int DoSomething(int &inputSize, int &outputSize, void (*progress)(int))
{
    progress(100);
    return 0;
}

int main()
{
    int inputSize = 3;
    int outputSize = 3;
    DoSomething(inputSize, outputSize, progressHandler);

    return 0;
}

Output:

received progress: 100

Even though I removed it (because I used g++) you can keep the __stdcall.

How to make a callback global so I can use it to other functions?

1 Answers1