1.\" Copyright (c) 1990, 1991 The Regents of the University of California. 2.\" All rights reserved. 3.\" 4.\" This code is derived from software contributed to Berkeley by 5.\" the American National Standards Committee X3, on Information 6.\" Processing Systems. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 3. All advertising materials mentioning features or use of this software 17.\" must display the following acknowledgement: 18.\" This product includes software developed by the University of 19.\" California, Berkeley and its contributors. 20.\" 4. Neither the name of the University nor the names of its contributors 21.\" may be used to endorse or promote products derived from this software 22.\" without specific prior written permission. 23.\" 24.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 25.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 26.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 27.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 28.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 29.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 30.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 31.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 32.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 33.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 34.\" SUCH DAMAGE. 35.\" 36.\" from: @(#)stdarg.3 6.8 (Berkeley) 6/29/91 37.\" $Id: stdarg.3,v 1.2 1993/08/01 07:37:10 mycroft Exp $ 38.\" 39.Dd June 29, 1991 40.Dt STDARG 3 41.Os 42.Sh NAME 43.Nm stdarg 44.Nd variable argument lists 45.Sh SYNOPSIS 46.Fd #include <stdarg.h> 47.Ft void 48.Fn va_start "va_list ap" last 49.Ft type 50.Fn va_arg "va_list ap" type 51.Ft void 52.Fn va_end "va_list ap" 53.Sh DESCRIPTION 54A function may be called with a varying number of arguments of varying 55types. 56The include file 57.Aq Pa stdarg.h 58declares a type 59.Pq Em va_list 60and defines three macros for stepping 61through a list of arguments whose number and types are not known to 62the called function. 63.Pp 64The called function must declare an object of type 65.Em va_list 66which is used by the macros 67.Fn va_start , 68.Fn va_arg , 69and 70.Fn va_end . 71.Pp 72The 73.Fn va_start 74macro initializes 75.Fa ap 76for subsequent use by 77.Fn va_arg 78and 79.Fn va_end , 80and must be called first. 81.Pp 82The parameter 83.Fa last 84is the name of the last parameter before the variable argument list, 85i.e. the last parameter of which the calling function knows the type. 86.Pp 87Because the address of this parameter is used in the 88.Fn va_start 89macro, it should not be declared as a register variable, or as a 90function or an array type. 91.Pp 92The 93.Fn va_start 94macro returns no value. 95.Pp 96The 97.Fn va_arg 98macro expands to an expression that has the type and value of the next 99argument in the call. 100The parameter 101.Fa ap 102is the 103.Em va_list Fa ap 104initialized by 105.Fn va_start . 106Each call to 107.Fn va_arg 108modifies 109.Fa ap 110so that the next call returns the next argument. 111The parameter 112.Fa type 113is a type name specified so that the type of a pointer to an 114object that has the specified type can be obtained simply by 115adding a * 116to 117.Fa type . 118.Pp 119If there is no next argument, or if 120.Fa type 121is not compatible with the type of the actual next argument 122(as promoted according to the default argument promotions), 123random errors will occur. 124.Pp 125The first use of the 126.Fn va_arg 127macro after that of the 128.Fn va_start 129macro returns the argument after 130.Fa last . 131Successive invocations return the values of the remaining 132arguments. 133.Pp 134The 135.Fn va_end 136macro handles a normal return from the function whose variable argument 137list was initialized by 138.Fn va_start . 139.Pp 140The 141.Fn va_end 142macro returns no value. 143.Sh EXAMPLES 144The function 145.Em foo 146takes a string of format characters and prints out the argument 147associated with each format character based on the type. 148.Bd -literal -offset indent 149void foo(char *fmt, ...) 150{ 151 va_list ap; 152 int d; 153 char c, *p, *s; 154 155 va_start(ap, fmt); 156 while (*fmt) 157 switch(*fmt++) { 158 case 's': /* string */ 159 s = va_arg(ap, char *); 160 printf("string %s\en", s); 161 break; 162 case 'd': /* int */ 163 d = va_arg(ap, int); 164 printf("int %d\en", d); 165 break; 166 case 'c': /* char */ 167 c = va_arg(ap, char); 168 printf("char %c\en", c); 169 break; 170 } 171 va_end(ap); 172} 173.Ed 174.Sh STANDARDS 175The 176.Fn va_start , 177.Fn va_arg , 178and 179.Fn va_end 180macros conform to 181.St -ansiC . 182.Sh COMPATIBILITY 183These macros are 184.Em not 185compatible with the historic macros they replace. 186A backward compatible version can be found in the include 187file 188.Aq Pa varargs.h . 189.Sh BUGS 190Unlike the 191.Em varargs 192macros, the 193.Nm stdarg 194macros do not permit programmers to 195code a function with no fixed arguments. 196This problem generates work mainly when converting 197.Em varargs 198code to 199.Nm stdarg 200code, 201but it also creates difficulties for variadic functions that 202wish to pass all of their arguments on to a function 203that takes a 204.Em va_list 205argument, such as 206.Xr vfprintf 3 . 207