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varargs(3)
NAME
  varargs, va_arg, va_start, va_end - Handle a variable-length parameter list

SYNOPSIS
  #include <varargs.h>

  va_alist
  va_dcl

  void va_start(
	  va_alist argp );

  type va_arg(
	  va_alist argp, type );

  void va_end(
	  va_alist argp );

LIBRARY
  Standard C Library (libc)

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

  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
  NOTE: When writing new code, it is recommended that you use stdarg instead
  of varargs. They both perform the same function, but stdarg is standards-
  compliant and varargs complies only with BSD conventions.

  The varargs 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 varargs macros, are inherently nonportable because different systems
  use different parameter-passing conventions.

  The varargs macros are as follows:

  va_start()
      Initializes argp to point to the beginning of the list. 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().

  va_alist()
      Is used in the function header to declare a variable argument list.
      va_dcl is a declaration for va_dcl. Note that there is no semicolon
      after va_dcl.

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 <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];
	  int argno = 0;
	  va_start(ap);
	  file = va_arg(ap, char *);
	  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), stdarg(3), vprintf(3)

Index for Section 3

Alphabetical listing for V

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