233 lines
5.8 KiB
Groff
233 lines
5.8 KiB
Groff
.\" Copyright (c) 1990, 1991, 1993
|
|
.\" The Regents of the University of California. All rights reserved.
|
|
.\"
|
|
.\" This code is derived from software contributed to Berkeley by
|
|
.\" the American National Standards Committee X3, on Information
|
|
.\" Processing Systems.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 3. All advertising materials mentioning features or use of this software
|
|
.\" must display the following acknowledgement:
|
|
.\" This product includes software developed by the University of
|
|
.\" California, Berkeley and its contributors.
|
|
.\" 4. Neither the name of the University nor the names of its contributors
|
|
.\" may be used to endorse or promote products derived from this software
|
|
.\" without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" @(#)stdarg.3 8.1 (Berkeley) 6/5/93
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd October 25, 2002
|
|
.Dt STDARG 3
|
|
.Os
|
|
.Sh NAME
|
|
.Nm stdarg
|
|
.Nd variable argument lists
|
|
.Sh SYNOPSIS
|
|
.In stdarg.h
|
|
.Ft void
|
|
.Fn va_start "va_list ap" last
|
|
.Ft type
|
|
.Fn va_arg "va_list ap" type
|
|
.Ft void
|
|
.Fn va_copy "va_list dest" "va_list src"
|
|
.Ft void
|
|
.Fn va_end "va_list ap"
|
|
.Sh DESCRIPTION
|
|
A function may be called with a varying number of arguments of varying
|
|
types.
|
|
The include file
|
|
.Aq Pa stdarg.h
|
|
declares a type
|
|
.Pq Em va_list
|
|
and defines three macros for stepping
|
|
through a list of arguments whose number and types are not known to
|
|
the called function.
|
|
.Pp
|
|
The called function must declare an object of type
|
|
.Em va_list
|
|
which is used by the macros
|
|
.Fn va_start ,
|
|
.Fn va_arg ,
|
|
.Fn va_copy ,
|
|
and
|
|
.Fn va_end .
|
|
.Pp
|
|
The
|
|
.Fn va_start
|
|
macro initializes
|
|
.Fa ap
|
|
for subsequent use by
|
|
.Fn va_arg
|
|
and
|
|
.Fn va_end ,
|
|
and must be called first.
|
|
.Pp
|
|
The parameter
|
|
.Fa last
|
|
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.
|
|
.Pp
|
|
Because the address of this parameter is used in the
|
|
.Fn va_start
|
|
macro, it should not be declared as a register variable, or as a
|
|
function or an array type.
|
|
.Pp
|
|
The
|
|
.Fn va_start
|
|
macro returns no value.
|
|
.Pp
|
|
The
|
|
.Fn va_arg
|
|
macro expands to an expression that has the type and value of the next
|
|
argument in the call.
|
|
The parameter
|
|
.Fa ap
|
|
is the
|
|
.Em va_list Fa ap
|
|
initialized by
|
|
.Fn va_start .
|
|
Each call to
|
|
.Fn va_arg
|
|
modifies
|
|
.Fa ap
|
|
so that the next call returns the next argument.
|
|
The parameter
|
|
.Fa type
|
|
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
|
|
adding a *
|
|
to
|
|
.Fa type .
|
|
.Pp
|
|
If there is no next argument, or if
|
|
.Fa type
|
|
is not compatible with the type of the actual next argument
|
|
(as promoted according to the default argument promotions),
|
|
random errors will occur.
|
|
.Pp
|
|
The first use of the
|
|
.Fn va_arg
|
|
macro after that of the
|
|
.Fn va_start
|
|
macro returns the argument after
|
|
.Fa last .
|
|
Successive invocations return the values of the remaining
|
|
arguments.
|
|
.Pp
|
|
The
|
|
.Fn va_copy
|
|
macro copies a variable argument list, previously initialized by
|
|
.Fn va_start ,
|
|
from
|
|
.Fa src
|
|
to
|
|
.Fa dest .
|
|
The state is preserved such that it is equivalent to calling
|
|
.Fn va_start
|
|
with the same second argument used with
|
|
.Fa src ,
|
|
and calling
|
|
.Fn va_arg
|
|
the same number of times as called with
|
|
.Fa src .
|
|
.Pp
|
|
The
|
|
.Fn va_copy
|
|
macro returns no value.
|
|
.Pp
|
|
The
|
|
.Fn va_end
|
|
macro handles a normal return from the function whose variable argument
|
|
list was initialized by
|
|
.Fn va_start .
|
|
.Pp
|
|
The
|
|
.Fn va_end
|
|
macro returns no value.
|
|
.Sh EXAMPLES
|
|
The function
|
|
.Em foo
|
|
takes a string of format characters and prints out the argument
|
|
associated with each format character based on the type.
|
|
.Bd -literal -offset indent
|
|
void foo(char *fmt, ...)
|
|
{
|
|
va_list ap;
|
|
int d;
|
|
char c, *s;
|
|
|
|
va_start(ap, fmt);
|
|
while (*fmt)
|
|
switch(*fmt++) {
|
|
case 's': /* string */
|
|
s = va_arg(ap, char *);
|
|
printf("string %s\en", s);
|
|
break;
|
|
case 'd': /* int */
|
|
d = va_arg(ap, int);
|
|
printf("int %d\en", d);
|
|
break;
|
|
case 'c': /* char */
|
|
/* Note: char is promoted to int. */
|
|
c = va_arg(ap, int);
|
|
printf("char %c\en", c);
|
|
break;
|
|
}
|
|
va_end(ap);
|
|
}
|
|
.Ed
|
|
.Sh STANDARDS
|
|
The
|
|
.Fn va_start ,
|
|
.Fn va_arg ,
|
|
.Fn va_copy ,
|
|
and
|
|
.Fn va_end
|
|
macros conform to
|
|
.St -isoC-99 .
|
|
.Sh COMPATIBILITY
|
|
These macros are
|
|
.Em not
|
|
compatible with the historic macros they replace.
|
|
A backward compatible version can be found in the include
|
|
file
|
|
.Aq Pa varargs.h .
|
|
.Sh BUGS
|
|
Unlike the
|
|
.Em varargs
|
|
macros, the
|
|
.Nm
|
|
macros do not permit programmers to
|
|
code a function with no fixed arguments.
|
|
This problem generates work mainly when converting
|
|
.Em varargs
|
|
code to
|
|
.Nm
|
|
code,
|
|
but it also creates difficulties for variadic functions that
|
|
wish to pass all of their arguments on to a function
|
|
that takes a
|
|
.Em va_list
|
|
argument, such as
|
|
.Xr vfprintf 3 .
|