The GNU C Library - Argument Macros

Argument Access Macros

Here are descriptions of the macros used to retrieve variable arguments. These macros are defined in the header file `stdarg.h'.

Data Type va_list

The type va_list is used for argument pointer variables.

Macro void va_start (va_list ap, last-required)

This macro initializes the argument pointer variable ap to point to the first of the optional arguments of the current function; last-required must be the last required argument to the function.

See Old Varargs, for an alternate definition of va_start found in the header file `varargs.h'.

Macro type va_arg (va_list ap, type)

The va_arg macro returns the value of the next optional argument, and modifies the value of ap to point to the subsequent argument. Thus, successive uses of va_arg return successive optional arguments.

The type of the value returned by va_arg is type as specified in the call. type must be a self-promoting type (not char or short int or float ) that matches the type of the actual argument.

Macro void va_end (va_list ap)

This ends the use of ap. After a va_end call, further va_arg calls with the same ap may not work. You should invoke va_end before returning from the function in which va_start was invoked with the same ap argument.

In the GNU C library, va_end does nothing, and you need not ever use it except for reasons of portability.