osf1 man page for stdarg

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)