1.\" $NetBSD: stdarg.3,v 1.4 1997/11/12 00:49:26 mrg Exp $ 2.\" 3.\" Copyright (c) 1990, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" This code is derived from software contributed to Berkeley by 7.\" the American National Standards Committee X3, on Information 8.\" Processing Systems. 9.\" 10.\" Redistribution and use in source and binary forms, with or without 11.\" modification, are permitted provided that the following conditions 12.\" are met: 13.\" 1. Redistributions of source code must retain the above copyright 14.\" notice, this list of conditions and the following disclaimer. 15.\" 2. Redistributions in binary form must reproduce the above copyright 16.\" notice, this list of conditions and the following disclaimer in the 17.\" documentation and/or other materials provided with the distribution. 18.\" 3. All advertising materials mentioning features or use of this software 19.\" must display the following acknowledgement: 20.\" This product includes software developed by the University of 21.\" California, Berkeley and its contributors. 22.\" 4. Neither the name of the University nor the names of its contributors 23.\" may be used to endorse or promote products derived from this software 24.\" without specific prior written permission. 25.\" 26.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 27.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 28.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 29.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 30.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 31.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 32.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 33.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 34.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 35.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 36.\" SUCH DAMAGE. 37.\" 38.\" @(#)stdarg.3 8.1 (Berkeley) 6/5/93 39.\" 40.Dd June 5, 1993 41.Dt STDARG 3 42.Os 43.Sh NAME 44.Nm stdarg , 45.Nm varargs , 46.Nm va_arg , 47.Nm va_end , 48.Nm va_start 49.Nd variable argument lists 50.Sh SYNOPSIS 51.Fd #include <stdarg.h> 52.Ft void 53.Fn va_start "va_list ap" last 54.Ft type 55.Fn va_arg "va_list ap" type 56.Ft void 57.Fn va_end "va_list ap" 58.Sh DESCRIPTION 59A function may be called with a varying number of arguments of varying 60types. 61The include file 62.Aq Pa stdarg.h 63declares a type 64.Pq Em va_list 65and defines three macros for stepping 66through a list of arguments whose number and types are not known to 67the called function. 68.Pp 69The called function must declare an object of type 70.Em va_list 71which is used by the macros 72.Fn va_start , 73.Fn va_arg , 74and 75.Fn va_end . 76.Pp 77The 78.Fn va_start 79macro initializes 80.Fa ap 81for subsequent use by 82.Fn va_arg 83and 84.Fn va_end , 85and must be called first. 86.Pp 87The parameter 88.Fa last 89is the name of the last parameter before the variable argument list, 90i.e. the last parameter of which the calling function knows the type. 91.Pp 92Because the address of this parameter is used in the 93.Fn va_start 94macro, it should not be declared as a register variable, or as a 95function or an array type. 96.Pp 97The 98.Fn va_start 99macro returns no value. 100.Pp 101The 102.Fn va_arg 103macro expands to an expression that has the type and value of the next 104argument in the call. 105The parameter 106.Fa ap 107is the 108.Em va_list Fa ap 109initialized by 110.Fn va_start . 111Each call to 112.Fn va_arg 113modifies 114.Fa ap 115so that the next call returns the next argument. 116The parameter 117.Fa type 118is a type name specified so that the type of a pointer to an 119object that has the specified type can be obtained simply by 120adding a * 121to 122.Fa type . 123.Pp 124If there is no next argument, or if 125.Fa type 126is not compatible with the type of the actual next argument 127(as promoted according to the default argument promotions), 128random errors will occur. 129.Pp 130The first use of the 131.Fn va_arg 132macro after that of the 133.Fn va_start 134macro returns the argument after 135.Fa last . 136Successive invocations return the values of the remaining 137arguments. 138.Pp 139The 140.Fn va_end 141macro handles a normal return from the function whose variable argument 142list was initialized by 143.Fn va_start . 144.Pp 145The 146.Fn va_end 147macro returns no value. 148.Sh EXAMPLES 149The function 150.Em foo 151takes a string of format characters and prints out the argument 152associated with each format character based on the type. 153.Bd -literal -offset indent 154void foo(char *fmt, ...) 155{ 156 va_list ap; 157 int d; 158 char c, *p, *s; 159 160 va_start(ap, fmt); 161 while (*fmt) 162 switch(*fmt++) { 163 case 's': /* string */ 164 s = va_arg(ap, char *); 165 printf("string %s\en", s); 166 break; 167 case 'd': /* int */ 168 d = va_arg(ap, int); 169 printf("int %d\en", d); 170 break; 171 case 'c': /* char */ 172 c = va_arg(ap, char); 173 printf("char %c\en", c); 174 break; 175 } 176 va_end(ap); 177} 178.Ed 179.Sh STANDARDS 180The 181.Fn va_start , 182.Fn va_arg , 183and 184.Fn va_end 185macros conform to 186.St -ansiC . 187.Sh COMPATIBILITY 188These macros are 189.Em not 190compatible with the historic macros they replace. 191A backward compatible version can be found in the include 192file 193.Aq Pa varargs.h . 194.Sh BUGS 195Unlike the 196.Em varargs 197macros, the 198.Nm stdarg 199macros do not permit programmers to 200code a function with no fixed arguments. 201This problem generates work mainly when converting 202.Em varargs 203code to 204.Nm stdarg 205code, 206but it also creates difficulties for variadic functions that 207wish to pass all of their arguments on to a function 208that takes a 209.Em va_list 210argument, such as 211.Xr vfprintf 3 . 212