stdarg(3) [osf1 man page]

stdarg(3)						     Library Functions Manual							 stdarg(3)

NAME

       stdarg - Handles a variable-length parameter list

LIBRARY

       Standard C Library (libc.so, libc.a)

SYNOPSIS

       #include <stdarg.h>

       va_list void va_start (	    va_list argp, parmN ); type va_arg (      va_list argp,	 type ); void va_end (	    va_list argp );

PARAMETERS

       argp   Specifies  a  variable  that  the stdarg macros use to keep track of the current location in the parameter list.	Do not modify this
	      variable.

       parmN  Specifies the last named parameter (the one just before the
	      "..." in the execl() definition in the Example section).	There must be at least one named parameter.

       type   Specifies the type to which the expected argument will be converted when passed as an argument.  Unsigned char  or  short  arguments
	      are  converted to unsigned int, and float arguments are converted to double.  Different types can be mixed, but it is up to the rou-
	      tine to know what type of argument is expected because the type cannot be determined at run time.

DESCRIPTION

       The stdarg set of macros allows you to write portable functions that accept a variable number of parameters. Subroutines  that  have  vari-
       able-length parameter lists (such as the printf() function), but that do not use the stdarg macros, are inherently nonportable because dif-
       ferent systems use different parameter-passing conventions.

       The stdarg macros are as follows:

       va_list
	      Defines the type of the variable used to traverse the list.

       va_start()
	      Initializes argp to point to the first unnamed argument.	The va_start() macro will be invoked before  any  access  to  the  unnamed
	      arguments.

       va_arg()
	      Returns the next parameter in the list pointed to by argp.

       va_end()
	      Cleans up at the end.

       Your  function  can  traverse,  or  scan, the parameter list more than once. Start each traversal with a call to va_start() and end it with
       va_end().

EXAMPLE

       The following example is a possible implementation of the execl() function: #include <stdarg.h> #define MAXargS 100 /* **  execl is  called
       by **  execl(file, arg1, arg2, . . . , (char *) 0); */ execl(char * file, . . .)  {  va_list ap;
	  char *file;
	  char *args[MAXargS];
	  int argno = 0;
	  va_start(ap, file);
	  while ((args[argno++] = va_arg(ap, char *)) != (char *) 0)
	     ;	 /* Empty loop body */
	  va_end(ap);
	  return (execv(file, args)); }

NOTES

       The  calling  routine  is  responsible for specifying the number of parameters because it is not always possible to determine this from the
       stack frame. For example, the execl() function is passed a null pointer to signal the end of the list. The printf() function determines the
       number of parameters from its fmt parameter.

       AES Support Level: Temporary use

RELATED INFORMATION

       Functions: exec(2), printf(3), varargs(3), vprintf(3) delim off

																	 stdarg(3)

Check Out this Related Man Page

varargs(3EXT)						    Extended Library Functions						     varargs(3EXT)

NAME

       varargs - handle variable argument list

SYNOPSIS

       #include <varargs.h>
       va_alist
       va_dcl
       va_list pvar;

       void va_start(va_listpvar);

       type va_arg(va_list pvar, type);

       void va_end(va_list pvar);

DESCRIPTION

       This set of macros allows portable procedures that accept variable argument lists to be written. Routines that have variable argument lists
       (such as printf(3C)) but do not use varargs are inherently non-portable, as different machines use different argument-passing conventions.

       va_alist is used as the parameter list in a function header.

       va_dcl is a declaration for va_alist. No semicolon should follow va_dcl.

       va_list is a type defined for the variable used to traverse the list.

       va_start is called to initialize pvar to the beginning of the list.

       va_arg will return the next argument in the list pointed to by pvar. type is the type the argument is expected to be. Different	types  can
       be mixed, but it is up to the routine to know what type of argument is expected, as it cannot be determined at runtime.

       va_end is used to clean up.

       Multiple traversals, each bracketed by va_start and va_end, are possible.

EXAMPLES

       Example 1: A sample program.

       This example is a possible implementation of execl (see exec(2) ).

	      #include <unistd.h>
	      #include <varargs.h>
	      #define MAXARGS	  100
	      /*   execl is called by
			execl(file, arg1, arg2, ..., (char *)0);
	      */
	      execl(va_alist)
	      va_dcl
	      {
		   va_list ap;
		   char *file;
		   char *args[MAXARGS]; 	 /* assumed big enough*/
		   int argno = 0;

		   va_start(ap);
		   file = va_arg(ap, char *);
		   while ((args[argno++] = va_arg(ap, char *)) != 0)
			;
		   va_end(ap);
		   return execv(file, args);
	      }

SEE ALSO

       exec(2), printf(3C), vprintf(3C), stdarg(3EXT)

NOTES

       It  is  up  to the calling routine to specify in some manner how many arguments there are, since it is not always possible to determine the
       number of arguments from the stack frame. For example, execl is passed a zero pointer to signal the end of the list. printf  can  tell  how
       many arguments are there by the format.

       It  is  non-portable  to  specify a second argument of char, short, or float to va_arg, since arguments seen by the called function are not
       char, short, or float. C converts char and short arguments to int and converts float arguments to double before passing them to a function.

       stdarg is the preferred interface.

SunOS 5.10							    10 May 2002 						     varargs(3EXT)

Linux and UNIX Man Pages

stdarg(3) [osf1 man page]

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