vscnprintf (9) - Linux Man Pages
vscnprintf: Format a string and place it in a buffer
vscnprintf - Format a string and place it in a buffer
*buf, size_t size, const char *fmt, va_list args);
- The buffer to place the result into
- The size of the buffer, including the trailing null space
- The format string to use
- Arguments for the format string
The return value is the number of characters which have been written into the buf not including the trailing '\0'. If size is == 0 the function returns 0.
If you're not already dealing with a va_list consider using scnprintf.