Using DllCall and Pass back Address to WIL

Keywords: 	 dllcall binary buffer

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Question:

I'm experimenting with writing customized DLLs in C++ to be used in our WinBatch scripts. I've written a DLL in C++ that passes back some numeric values to the WinBatch script. A sample DllCall statement I've used is

	b=0
	a1=dllcall(dllname, void:"MyTest", word:b)
	Message("b is ", b)

The MyTest function in the DLL returns some calculated value. The C++ Dll looks like this:

	__declspec(dllexport) void WINAPI PASCAL MyTest(int* len)
	{ int i;
	i = 43;
	*len = i;
	}

The Dll compiles and links ok but when I run the WinBatch, the value of b is displayed as 0 not the expected 43. I have success passing back string values using char* and lpbinary but not with int* and long (or word). Any ideas what I am missing?

If I forget the b=0 statement before the dllcall, WinBatch aborts with a "Tag Overwrite 1" error message. But I guess that is supposed to happen.

Answer:

This should work:

bb=BinaryAlloc(4)
BinaryEODSet(bb,4)
a1=dllcall(dllname, void:"MyTest", lpbinary:bb)
b=BinaryPeek4(bb,0)
BinaryFree(bb)
Message("b is ", b)

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Article ID:   W12870

Filename:   Using Dll Created in C to Pass Address.txt