PROLOG | NAME | SYNOPSIS | DESCRIPTION | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

stdarg.h(0P)              POSIX Programmer's Manual             stdarg.h(0P)

PROLOG         top

       This manual page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior), or
       the interface may not be implemented on Linux.

NAME         top

       stdarg.h — handle variable argument list

SYNOPSIS         top

       #include <stdarg.h>

       void va_start(va_list ap, argN);
       void va_copy(va_list dest, va_list src);
       type va_arg(va_list ap, type);
       void va_end(va_list ap);

DESCRIPTION         top

       The functionality described on this reference page is aligned with
       the ISO C standard. Any conflict between the requirements described
       here and the ISO C standard is unintentional. This volume of
       POSIX.1‐2008 defers to the ISO C standard.

       The <stdarg.h> header shall contain a set of macros which allows
       portable functions that accept variable argument lists to be written.
       Functions that have variable argument lists (such as printf()) but do
       not use these macros are inherently non-portable, as different
       systems use different argument-passing conventions.

       The <stdarg.h> header shall define the va_list type for variables
       used to traverse the list.

       The va_start() macro is invoked to initialize ap to the beginning of
       the list before any calls to va_arg().

       The va_copy() macro initializes dest as a copy of src, as if the
       va_start() macro had been applied to dest followed by the same
       sequence of uses of the va_arg() macro as had previously been used to
       reach the present state of src.  Neither the va_copy() nor va_start()
       macro shall be invoked to reinitialize dest without an intervening
       invocation of the va_end() macro for the same dest.

       The object ap may be passed as an argument to another function; if
       that function invokes the va_arg() macro with parameter ap, the value
       of ap in the calling function is unspecified and shall be passed to
       the va_end() macro prior to any further reference to ap.  The
       parameter argN is the identifier of the rightmost parameter in the
       variable parameter list in the function definition (the one just
       before the ...). If the parameter argN is declared with the register
       storage class, with a function type or array type, or with a type
       that is not compatible with the type that results after application
       of the default argument promotions, the behavior is undefined.

       The va_arg() macro shall return the next argument in the list pointed
       to by ap.  Each invocation of va_arg() modifies ap so that the values
       of successive arguments are returned in turn. The type parameter
       shall be a type name specified such that the type of a pointer to an
       object that has the specified type can be obtained simply by
       postfixing a '*' to type. If there is no actual next argument, or if
       type is not compatible with the type of the actual next argument (as
       promoted according to the default argument promotions), the behavior
       is undefined, except for the following cases:

        *  One type is a signed integer type, the other type is the
           corresponding unsigned integer type, and the value is
           representable in both types.

        *  One type is a pointer to void and the other is a pointer to a
           character type.

        *  Both types are pointers.

       Different types can be mixed, but it is up to the routine to know
       what type of argument is expected.

       The va_end() macro is used to clean up; it invalidates ap for use
       (unless va_start() or va_copy() is invoked again).

       Each invocation of the va_start() and va_copy() macros shall be
       matched by a corresponding invocation of the va_end() macro in the
       same function.

       Multiple traversals, each bracketed by va_start() ...  va_end(), are
       possible.

       The following sections are informative.

EXAMPLES         top

       This example is a possible implementation of execl():

           #include <stdarg.h>

           #define  MAXARGS     31

           /*
            * execl is called by
            * execl(file, arg1, arg2, ..., (char *)(0));
            */
           int execl(const char *file, const char *args, ...)
           {
               va_list ap;
               char *array[MAXARGS +1];
               int argno = 0;

               va_start(ap, args);
               while (args != 0 && argno < MAXARGS)
               {
                   array[argno++] = args;
                   args = va_arg(ap, const char *);
               }
               array[argno] = (char *) 0;
               va_end(ap);
               return execv(file, array);
           }

APPLICATION USAGE         top

       It is up to the calling routine to communicate to the called routine
       how many arguments there are, since it is not always possible for the
       called routine to determine this in any other way. For example,
       execl() is passed a null pointer to signal the end of the list. The
       printf() function can tell how many arguments are there by the format
       argument.

RATIONALE         top

       None.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       The System Interfaces volume of POSIX.1‐2008, exec(1p), fprintf(3p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) In the event of any discrepancy between this version and
       the original IEEE and The Open Group Standard, the original IEEE and
       The Open Group Standard is the referee document. The original
       Standard can be obtained online at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the
       source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                 2013                        stdarg.h(0P)

Pages that refer to this page: stdio.h(0p)wchar.h(0p)wctype.h(0p)va_arg(3p)vfprintf(3p)vfscanf(3p)vfwprintf(3p)vfwscanf(3p)