How to define a function pointer for "SendMessageCallbackA"??

[Test Test]

The original definition of "SendMessageCallbackA" is:
WINUSERAPI
BOOL
WINAPI
SendMessageCallbackA(
IN HWND hWnd,
IN UINT Msg,
IN WPARAM wParam,
IN LPARAM lParam,
IN SENDASYNCPROC lpResultCallBack,
IN ULONG_PTR dwData);

And the definition of "SENDASYNCPROC" is:
typedef VOID (CALLBACK* SENDASYNCPROC)(HWND, UINT, ULONG_PTR, LRESULT);

Now I want to define a function pointer for "SendMessageCallbackA":
BOOL (WINAPI * Real_SendMessageCallbackA)(HWND hWnd, UINT Msg, WPARAM wParam, LPARAM lParam, SENDASYNCPROC lpResultCallBack, ULONG_PTR dwData)
=SendMessageCallbackA;

But I get an error when I compile the file:
error C2440: 'initializing' : cannot convert from '' to 'int (__stdcall *)(struct HWND__ *,unsigned int,unsigned int,long,void (__stdcall *)(struct HWND__ *,unsigned int,unsigned long,long),void *)'
None of the functions with this name in scope match the target type

I couldn't find what the problem is.
What's wrong with my code? How could I define a function pointer for "SendMessageCallbackA"? Who can help me?

Thanks a lot!!

[webJose]

Should be &SendMessageCallbackA, I would say, assuming your pointer declaration is OK. Some compilers take it as you wrote it, but it is not the standard AFAIK.

[Computergeek01]

Is this just for practice or is there some unusual reason that you are doing it this way? I ask because User32.dll is included in Windows apps running in User space so defining a function pointer to it feels redundent.

[andywestken]

I find your code compiles file, for what it's worth. As does webJose & version.

The '' is "error C2440: 'initializing' : cannot convert from '' to ..." is a bit strange, as is the final void* (cf. ULONG_PTR)?

I'm also curious why you need to get at SendMessageCallback in this way.

Andy

[Test Test]

Thank you, webJose! I find what the problem is using your method!

After the compilation, the format of the function "SendMessageCallbackA" becomes:
int (__stdcall *)(struct HWND__ *,unsigned int,unsigned int,long,void (__stdcall *)(struct HWND__ *,unsigned int,unsigned long,long),unsigned long)

However, after the compilation, the format of the function pointer "Real_SendMessageCallbackA" becomes:
int (__stdcall *)(struct HWND__ *,unsigned int,unsigned int,long,void (__stdcall *)(struct HWND__ *,unsigned int,unsigned long,long),void *)

See the last parameter, which is different.
Thus, I use a new method to define the function pointer which is successful:
BOOL (WINAPI * Real_SendMessageCallbackA)(HWND hWnd, UINT Msg, WPARAM wParam, LPARAM lParam, SENDASYNCPROC lpResultCallBack, ULONG dwData)
=SendMessageCallbackA;

Computergeek01 and andywestken, thank you anyway!
Do you know the "Detours" tool which will define the "Trampolines" functions?
I use the tool to do some work, which requires to define a function pointer to "SendMessageCallbackA".

Thank all of you again!!

[andywestken]

Ah - Detours. The Microsoft Research binary interception toolkit.

http://research.microsoft.com/en-us/projects/detours/

I did look into it when it was first released, when I had some performance problems to look at. But you have to pay to use it for non-eductation/non-research uses. And as I needed it for a commercial development project, but couldn't justify the cost for one-off use, ended up having to relay on custom code instead :-(.

The system I was looking at was too complicated for TrueTime - which was available - to handle (processing which took tens of minutes took 24+ hours under TrueTime with full instrumentation).