.TH VARARGS 3
.CT 2 data_man
.SH NAME
varargs \(mi variable argument list
.SH SYNOPSIS
.nf
.B #include <varargs.h>
.IB function (va_alist)
.B va_dcl
.PP
.B va_list  pvar;
.PP
.B va_start(pvar);
.PP
.B va_arg(pvar, type);
.PP
.B va_end(pvar);
.fi
.SH DESCRIPTION
This set of macros allows portable procedures that accept variable
argument lists to be written.
Routines which have variable argument lists (such as
.IR printf (3))
that do not use varargs are inherently nonportable, since different
machines use different argument passing conventions.
.PP
The literal identifier
.I va_alist
is used in a function header to declare a variable argument list.
It is declared by
.I va_dcl.
Note that there is no semicolon after
.I va_dcl.
.PP
.B Va_list
is the type of the variable
.I pvar,
which is used to traverse the list.
One variable of this type must always be declared.
.PP
.I Va_start
initializes
.I pvar
to the beginning of the list.
.PP
.I Va_arg
returns the next argument in the list
pointed to by
.IR pvar .
.I Type
is the type the argument is expected to be.
Different types can be mixed, but it is up
to the routine to know what type is
expected, since it cannot be determined at runtime.
.PP
.I Va_end
is used to finish up.
.PP
Multiple traversals, each bracketed by
.I va_start
and
.I va_end,
are possible.
.SH EXAMPLES
How to define
.I execl
in terms of
.IR execv ;
see
.IR exec (2):
.IP
.nf
.ft L
#include <varargs.h>
execl(va_alist)
va_dcl
{
	va_list ap;
	char *file;
	char *args[100];
	int argno = 0;
	va_start(ap);
	file = va_arg(ap, char*);
	while(args[argno++] = va_arg(ap, char*));
	va_end(ap);
	execv(file, args);
}
.fi
.ft P