C Standard Library: 7 Variable Argument Lists: <stdarg.h>

7 Variable Argument Lists: <stdarg.h>

The header <stdarg.h> provides facilities for stepping through a list of function arguments of
unknown number and type.
Suppose lastarg is the last named parameter of a function f with a variable number of
arguments. Then declare within f a variable of type va_list that will point to each argument
in turn:
va_list ap;
ap must be initialized once with the macro va_start before any unnamed argument is
accessed:
va_start(va_list ap, lastarg);
Thereafter, each execution of the macro va_arg will produce a value that has the type and
value of the next unnamed argument, and will also modify ap so the next use of va_arg returns
the next argument:
type va_arg(va_list ap, type);
The macro
void va_end(va_list ap);
must be called once after the arguments have been processed but before f is exited.