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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.\" @(#)stdarg.3 8.1 (Berkeley) 6/5/93 37.\" $FreeBSD$ 38.\" 39.Dd October 25, 2002 40.Dt STDARG 3 41.Os 42.Sh NAME 43.Nm stdarg 44.Nd variable argument lists 45.Sh SYNOPSIS 46.In 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_copy "va_list dest" "va_list src" 53.Ft void 54.Fn va_end "va_list ap" 55.Sh DESCRIPTION 56A function may be called with a varying number of arguments of varying 57types. 58The include file 59.In stdarg.h 60declares a type 61.Pq Em va_list 62and defines four macros for stepping 63through a list of arguments whose number and types are not known to 64the called function. 65.Pp 66The called function must declare an object of type 67.Em va_list 68which is used by the macros 69.Fn va_start , 70.Fn va_arg , 71.Fn va_copy , 72and 73.Fn va_end . 74.Pp 75The 76.Fn va_start 77macro initializes 78.Fa ap 79for subsequent use by 80.Fn va_arg , 81.Fn va_copy , 82and 83.Fn va_end , 84and must be called first. 85.Pp 86The parameter 87.Fa last 88is the name of the last parameter before the variable argument list, 89i.e., the last parameter of which the calling function knows the type. 90.Pp 91Because the address of this parameter is used in the 92.Fn va_start 93macro, it should not be declared as a register variable, or as a 94function or an array type. 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 106or 107.Fn va_copy . 108Each call to 109.Fn va_arg 110modifies 111.Fa ap 112so that the next call returns the next argument. 113The parameter 114.Fa type 115is a type name specified so that the type of a pointer to an 116object that has the specified type can be obtained simply by 117adding a * 118to 119.Fa type . 120.Pp 121If there is no next argument, or if 122.Fa type 123is not compatible with the type of the actual next argument 124(as promoted according to the default argument promotions), 125random errors will occur. 126.Pp 127The first use of the 128.Fn va_arg 129macro after that of the 130.Fn va_start 131macro returns the argument after 132.Fa last . 133Successive invocations return the values of the remaining 134arguments. 135.Pp 136The 137.Fn va_copy 138macro copies a variable argument list, previously initialized by 139.Fn va_start , 140from 141.Fa src 142to 143.Fa dest . 144The state is preserved such that it is equivalent to calling 145.Fn va_start 146with the same second argument used with 147.Fa src , 148and calling 149.Fn va_arg 150the same number of times as called with 151.Fa src . 152.Pp 153The 154.Fn va_end 155macro cleans up any state associated with the variable argument list 156.Fa ap . 157.Pp 158Each invocation of 159.Fn va_start 160or 161.Fn va_copy 162must be paired with a corresponding invocation of 163.Fn va_end 164in the same function. 165.Sh RETURN VALUES 166The 167.Fn va_arg 168macro returns the value of the next argument. 169.Pp 170The 171.Fn va_start , 172.Fn va_copy , 173and 174.Fn va_end 175macros return no value. 176.Sh EXAMPLES 177The function 178.Em foo 179takes a string of format characters and prints out the argument 180associated with each format character based on the type. 181.Bd -literal -offset indent 182void foo(char *fmt, ...) 183{ 184 va_list ap; 185 int d; 186 char c, *s; 187 188 va_start(ap, fmt); 189 while (*fmt) 190 switch(*fmt++) { 191 case 's': /* string */ 192 s = va_arg(ap, char *); 193 printf("string %s\en", s); 194 break; 195 case 'd': /* int */ 196 d = va_arg(ap, int); 197 printf("int %d\en", d); 198 break; 199 case 'c': /* char */ 200 /* Note: char is promoted to int. */ 201 c = va_arg(ap, int); 202 printf("char %c\en", c); 203 break; 204 } 205 va_end(ap); 206} 207.Ed 208.Sh COMPATIBILITY 209These macros are 210.Em not 211compatible with the historic macros they replace. 212A backward compatible version can be found in the include 213file 214.In varargs.h . 215.Sh STANDARDS 216The 217.Fn va_start , 218.Fn va_arg , 219.Fn va_copy , 220and 221.Fn va_end 222macros conform to 223.St -isoC-99 . 224.Sh BUGS 225Unlike the 226.Em varargs 227macros, the 228.Nm 229macros do not permit programmers to 230code a function with no fixed arguments. 231This problem generates work mainly when converting 232.Em varargs 233code to 234.Nm 235code, 236but it also creates difficulties for variadic functions that 237wish to pass all of their arguments on to a function 238that takes a 239.Em va_list 240argument, such as 241.Xr vfprintf 3 . 242