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stdarg(3)
NAME
  stdarg - Handle a variable-length parameter list

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 );

LIBRARY
  Standard C Library (libc)

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 routine 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 variable-length
  parameter lists (such as the printf() function), but that do not use the
  stdarg macros, are inherently nonportable because different 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().

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

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));
       }

SEE ALSO
  Functions: exec(2), printf(3), varargs(3), vprintf(3)

Index for Section 3

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