Variable Length Argument Lists

Akin to the Python [args](/cs-notes/Programming/Python/args%20and%20**kwargs.html), the ... in C signifies a variable length argument list, aka a function that takes in practically infinite arguments.

If we take a look at the declaration of printf(), we might see this:

int printf(char *fmt, ...)

Note that the ... notation only appears at the end of the function argument list. The behavior of this notation is defined in stdarg.h. A type va_list is used to refer to each argument sequentially. Then the va_start macro initializes your va_list type variable (say we call it ap)to the first item in the first unnamed argument. It must be used once before ap is used. There must be at least one named argument, in the case of printf(), it’s char* fmt.

If you have a va_start, va_end cleans everything up.

#C #C/features