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STDARG(3)		     Library Functions Manual		       STDARG(3)

NAME
     stdarg -- variable argument lists

SYNOPSIS
     #include <stdarg.h>

     void
     va_start(va_list ap, last);

     type
     va_arg(va_list ap, type);

     void
     va_copy(va_list dest, va_list src);

     void
     va_end(va_list ap);

DESCRIPTION
     A	function  may  be  called  with a varying number of arguments of varying
     types.  The include file <stdarg.h> declares a type (va_list)  and  defines
     four macros for stepping through a list of arguments whose number and types
     are not known to the called function.

     The called function must declare an object of type va_list which is used by
     the macros va_start(), va_arg(), va_copy(), and va_end().

     The  va_start()  macro  initializes  ap  for  subsequent  use  by va_arg(),
     va_copy(), and va_end(), and must be called first.

     The parameter last is the name of the last parameter  before  the	variable
     argument list, i.e., the last parameter of which the calling function knows
     the type.

     Because  the  address of this parameter is used in the va_start() macro, it
     should not be declared as a register variable, or as a function or an array
     type.

     The va_arg() macro expands to an expression that has the type and value  of
     the next argument in the call.  The parameter ap is the va_list ap initial-
     ized by va_start() or va_copy().  Each call to va_arg() modifies ap so that
     the next call returns the next argument.  The parameter type is a type name
     specified so that the type of a pointer to an object that has the specified
     type can be obtained simply by adding a * to type.

     If there is no next argument, or if type is not compatible with the type of
     the  actual  next	argument  (as promoted according to the default argument
     promotions), random errors will occur.

     The first use of the va_arg() macro after that of the va_start() macro  re-
     turns the argument after last.  Successive invocations return the values of
     the remaining arguments.

     The va_copy() macro copies a variable argument list, previously initialized
     by  va_start(),  from  src to dest.  The state is preserved such that it is
     equivalent to calling va_start() with the same second  argument  used  with
     src, and calling va_arg() the same number of times as called with src.

     The  va_end()  macro cleans up any state associated with the variable argu-
     ment list ap.

     Each invocation of va_start() or va_copy() must be  paired  with  a  corre-
     sponding invocation of va_end() in the same function.

RETURN VALUES
     The va_arg() macro returns the value of the next argument.

     The va_start(), va_copy(), and va_end() macros return no value.

EXAMPLES
     The function foo takes a string of format characters and prints out the ar-
     gument associated with each format character based on the type.

	   void foo(char *fmt, ...)
	   {
		   va_list ap;
		   int d;
		   char c, *s;

		   va_start(ap, fmt);
		   while (*fmt)
			   switch(*fmt++) {
			   case 's':			   /* string */
				   s = va_arg(ap, char *);
				   printf("string %s\n", s);
				   break;
			   case 'd':			   /* int */
				   d = va_arg(ap, int);
				   printf("int %d\n", d);
				   break;
			   case 'c':			   /* char */
				   /* Note: char is promoted to int. */
				   c = va_arg(ap, int);
				   printf("char %c\n", c);
				   break;
			   }
		   va_end(ap);
	   }

COMPATIBILITY
     These macros are not compatible with the historic macros they replace.

STANDARDS
     The va_start(), va_arg(), va_copy(), and va_end() macros conform to ISO/IEC
     9899:1999 ("ISO C99").

HISTORY
     The  va_start(),  va_arg()  and  va_end()	macros	were  introduced in ANSI
     X3.159-1989 ("ANSI C89").	The va_copy() macro was  introduced  in  ISO/IEC
     9899:1999 ("ISO C99").

BUGS
     Unlike  the  varargs macros, the stdarg macros do not permit programmers to
     code a function with no  fixed  arguments.   This	problem  generates  work
     mainly  when  converting  varargs	code to stdarg code, but it also creates
     difficulties for variadic functions that wish to pass all	of  their  argu-
     ments on to a function that takes a va_list argument, such as vfprintf(3).

FreeBSD 15.1			October 18, 2024		       STDARG(3)
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