On a machine's runtime stack, there is no indication of how many parameters were passed to the function (at least on x86). C functions must use one of the mand

On a machine's runtime stack, there is no indication of how many parameters were passed to the function (at least on x86). C functions must use one of the mandatory arguments to determine how many arguments were pushed on the stack. In the case of the printf-family of functions, it's the number of format specifiers, e.g., "%d".