.\" Copyright (c) 1990, 1991 The Regents of the University of California.
.\" This code is derived from software contributed to Berkeley by
.\" the American National Standards Committee X3, on Information
.\" %sccs.include.redist.man%
.\" @(#)stdarg.3 6.8 (Berkeley) %G%
.Nd variable argument lists
.Fn va_start "va_list ap" last
.Fn va_arg "va_list ap" type
A function may be called with a varying number of arguments of varying
and defines three macros for stepping
through a list of arguments whose number and types are not known to
The called function must declare an object of type
which is used by the macros
and must be called first.
is the name of the last parameter before the variable argument list,
i.e. the last parameter of which the calling function knows the type.
Because the address of this parameter is used in the
macro, it should not be declared as a register variable, or as a
function or an array type.
macro expands to an expression that has the type and value of the next
so that the next call returns the next argument.
is a type name specified so that the type of a pointer to an
object that has the specified type can be obtained simply by
If there is no next argument, or if
is not compatible with the type of the actual next argument
(as promoted according to the default argument promotions),
random errors will occur.
macro returns the argument after
Successive invocations return the values of the remaining
macro handles a normal return from the function whose variable argument
takes a string of format characters and prints out the argument
associated with each format character based on the type.
.Bd -literal -offset indent
printf("string %s\en", s);
compatible with the historic macros they replace.
A backward compatible version can be found in the include
macros do not permit programmers to
code a function with no fixed arguments.
This problem generates work mainly when converting
but it also creates difficulties for variadic functions that
wish to pass all of their arguments on to a function