Format a string and place it in a buffer
int vsprintf(char * buf, const char * fmt, va_list args);
buf
The buffer to place the result into
fmt
The format string to use
args
Arguments for the format string
The function returns the number of characters written into buf. Use vsnprintf or vscnprintf in order to avoid buffer overflows.
If you're not already dealing with a va_list consider using sprintf.
See the vsnprintf documentation for format string extensions over C99.