_vscprintf help

I'm trying to make a printf like function for writing output to a log file. I was looking at MSDN for some help and found the _vscprintf function for making the buffer large enough to hold the data. It says it's in stdio.h, but my stdio.h does not have that function. I've searched the entire include folder for the function and found nothing except for one in the platform sdk for win64 stuff. I'm using Visual C++ 6.0. Has anyone else had a problem like this? Any ideas on how to get it working? Anything would be appreciated.