Call external procedure by address

[penagate]

What is the C++ command to call a procedure (residing in a calling app) by its address, in a function that accepts the address (of the function to be called) as an argument?

Usage: To call a VB procedure by its address using a C++ DLL.
e.g.

Private declare sub CallByProcAddress Lib "xxx" (ByVal lpfnProcAddress as Long)
 
CallByProcAddress AddressOf TheProc

Sorry, I'm a C++ n00b.

[sunburnt]

You can do something like this: (assuming the function you want to call is int __stdcall somefunc(int a, int b) )

typdef int (__stdcall* myfunctionptr)(int a, int b);

int call_myfunc(void* ptr, int arga, int argb)
{
   ((myfunctionptr) _ptr = (myfunctionptr)ptr;
   return _ptr(arga, argb);
}

basically you cast the address to a function pointer.

[penagate]

Couldn't get it to work... it said _ptr was an undefined identifier.

Could you please possibly explain to me how to do it.. then I will understand a bit better?

Sorry for being such a newb

[sunburnt]

Not your fault -- looks like I messed up

Give this a try; I'm not sure what I was thinking when I wrote that.

typdef int (__stdcall* myfunctionptr)(int a, int b);

int call_myfunc(void* ptr, int arga, int argb)
{
   myfunctionptr _ptr = (myfunctionptr)ptr;
   return _ptr(arga, argb);
}

[penagate]

I built it, it failed...
I changed typdef to typedef , added an export file, built it again, and it made a DLL file fine... but then when I tried to call it from VB the IDE crashed

Does void* ptr mean I pass the address of the function as a Long (from VB)?
I'm not sure how to declare it.

[penagate]

I changed it a bit, not sure what did the trick, but it works now

Here is the code I finished with:

int __stdcall CallByProcAddress(void* lpfnProcAddress, long arga, long argb)
{
   ProcAddress _lpfnProcAddress = (ProcAddress)lpfnProcAddress;
   return _lpfnProcAddress(arga, argb);
}

Public Declare Function CallByProcAddress Lib "xxxx" _
    (ByVal lpfnProcAddress As Long, _
     ByVal arga As Long, _
     ByVal argb As Long) _
    As Integer

Thanks, I kinda understand it now