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Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)stdarg.3 8.1 (Berkeley) 6/5/93 33.\" $FreeBSD: src/share/man/man3/stdarg.3,v 1.15 2005/01/21 08:36:36 ru Exp $ 34.\" 35.Dd May 9, 2019 36.Dt STDARG 3 37.Os 38.Sh NAME 39.Nm stdarg 40.Nd variable argument lists 41.Sh SYNOPSIS 42.In stdarg.h 43.Ft void 44.Fn va_start "va_list ap" last 45.Ft type 46.Fn va_arg "va_list ap" type 47.Ft void 48.Fn va_copy "va_list dest" "va_list src" 49.Ft void 50.Fn va_end "va_list ap" 51.Sh DESCRIPTION 52A function may be called with a varying number of arguments of varying 53types. 54The include file 55.In stdarg.h 56declares a type 57.Pq Em va_list 58and defines three macros for stepping 59through a list of arguments whose number and types are not known to 60the called function. 61.Pp 62The called function must declare an object of type 63.Em va_list 64which is used by the macros 65.Fn va_start , 66.Fn va_arg , 67.Fn va_copy , 68and 69.Fn va_end . 70.Pp 71The 72.Fn va_start 73macro initializes 74.Fa ap 75for subsequent use by 76.Fn va_arg 77and 78.Fn va_end , 79and must be called first. 80.Pp 81The parameter 82.Fa last 83is the name of the last parameter before the variable argument list, 84i.e., the last parameter of which the calling function knows the type. 85.Pp 86Because the address of this parameter is used in the 87.Fn va_start 88macro, it should not be declared as a register variable, or as a 89function or an array type. 90.Pp 91The 92.Fn va_start 93macro returns no value. 94.Pp 95The 96.Fn va_arg 97macro expands to an expression that has the type and value of the next 98argument in the call. 99The parameter 100.Fa ap 101is the 102.Em va_list Fa ap 103initialized by 104.Fn va_start . 105Each call to 106.Fn va_arg 107modifies 108.Fa ap 109so that the next call returns the next argument. 110The parameter 111.Fa type 112is a type name specified so that the type of a pointer to an 113object that has the specified type can be obtained simply by 114adding a * 115to 116.Fa type . 117.Pp 118If there is no next argument, or if 119.Fa type 120is not compatible with the type of the actual next argument 121(as promoted according to the default argument promotions), 122random errors will occur. 123.Pp 124The first use of the 125.Fn va_arg 126macro after that of the 127.Fn va_start 128macro returns the argument after 129.Fa last . 130Successive invocations return the values of the remaining 131arguments. 132.Pp 133The 134.Fn va_copy 135macro copies a variable argument list, previously initialized by 136.Fn va_start , 137from 138.Fa src 139to 140.Fa dest . 141The state is preserved such that it is equivalent to calling 142.Fn va_start 143with the same second argument used with 144.Fa src , 145and calling 146.Fn va_arg 147the same number of times as called with 148.Fa src . 149.Pp 150The 151.Fn va_copy 152macro returns no value. 153.Pp 154The 155.Fn va_end 156macro handles a normal return from the function whose variable argument 157list was initialized by 158.Fn va_start . 159.Pp 160The 161.Fn va_end 162macro returns no value. 163.Sh EXAMPLES 164The function 165.Em foo 166takes a string of format characters and prints out the argument 167associated with each format character based on the type. 168.Bd -literal -offset indent 169void foo(char *fmt, ...) 170{ 171 va_list ap; 172 int d; 173 char c, *s; 174 175 va_start(ap, fmt); 176 while (*fmt) 177 switch(*fmt++) { 178 case 's': /* string */ 179 s = va_arg(ap, char *); 180 printf("string %s\en", s); 181 break; 182 case 'd': /* int */ 183 d = va_arg(ap, int); 184 printf("int %d\en", d); 185 break; 186 case 'c': /* char */ 187 /* Note: char is promoted to int. */ 188 c = va_arg(ap, int); 189 printf("char %c\en", c); 190 break; 191 } 192 va_end(ap); 193} 194.Ed 195.Sh COMPATIBILITY 196These macros are 197.Em not 198compatible with the historic macros they replace. 199.Sh STANDARDS 200The 201.Fn va_start , 202.Fn va_arg , 203.Fn va_copy , 204and 205.Fn va_end 206macros conform to 207.St -isoC-99 . 208.Sh BUGS 209Unlike the 210.Em varargs 211macros, the 212.Nm 213macros do not permit programmers to 214code a function with no fixed arguments. 215This problem generates work mainly when converting 216.Em varargs 217code to 218.Nm 219code, 220but it also creates difficulties for variadic functions that 221wish to pass all of their arguments on to a function 222that takes a 223.Em va_list 224argument, such as 225.Xr vfprintf 3 . 226