I've included the only two required header files (stdio.h and wchar.h) that MSDN says are required by this function. I'm getting the undeclared function error. For some reason I can't seem to use many of the functions beginning with an underscore such as _vscprintf. This function is exactly what i need.

Nevermind. I've been helped. That particular function isn't available in VC 6. Instead I used _vsnprintf().