Pass a __thiscall to a function typedef

Question

I don't even know how to properly word this, but I'll try my best to explain it in code:

typedef void( *ExampleFn )( PVOID p1, PVOID p2, PVOID p3 );

struct Example
{
    void ExampleFunction( PVOID p1, PVOID p2, PVOID p3 )
    {
        // do something with Example's members
    }
};

Example example;
ExampleFn exampleFn = example.ExampleFunction;

So, I get this error:

Error C2440 '=': cannot convert from 'void (__thiscall Example::* )(PVOID,PVOID,PVOID)' to 'ExampleFn'

I understand the problem, Example::ExampleFunction is a __thiscall and ExampleFn is not, but how can I go about this?

How to have a Example object with a ExampleFn-like function in it that can use that object's members?

Supposed that you can use one of the `PVOID` parameters to pass user defined data, the marked duplicate's answers offer a way how it can be done. — πάντα ῥεῖ, Oct 22 '15 at 15:37

Klemens Morgenstern · Answer 1 · 2015-10-22T15:34:13.270

1

You need to define youre function-pointer correctly. It's a member-function pointer, so it needs to look like this:

typedef void(Example::*ExampleFn )( PVOID p1, PVOID p2, PVOID p3 );

The __thiscall is just the call-convention of member-functions, so that's set automatically.

You defined a pointer to a plain-function so it doesn't work. That doesn't concern the call-convetion really.

edited Oct 22 '15 at 15:34

answered Oct 22 '15 at 15:31

Klemens Morgenstern

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Let's say that I cannot change that ExampleFn. I don't have control over how to define it. – user3260957 Oct 22 '15 at 15:33
Then you cannot bind a member-function to it, it's ought to be a plain function or a static member function. – Klemens Morgenstern Oct 22 '15 at 15:34
That's what I thought, I was just wondering if there's a way to do this. – user3260957 Oct 22 '15 at 15:39
Not really, because a method needs the this-pointes as an additional argument. You might consider using std::function with a std::bind or a lambda. – Klemens Morgenstern Oct 22 '15 at 15:57

Pass a __thiscall to a function typedef

1 Answers1