gcc/doc/gcc/extensions-to-the-c-language-family/pointer-arguments-in-variadic-functions.rst

   1 ..
   2   Copyright 1988-2022 Free Software Foundation, Inc.
   3   This is part of the GCC manual.
   4   For copying conditions, see the copyright.rst file.
   5
   6 .. index:: pointer arguments in variadic functions, variadic functions, pointer arguments
   7
   8 .. _variadic-pointer-args:
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  10 Pointer Arguments in Variadic Functions
  11 ***************************************
  12
  13 Standard C requires that pointer types used with ``va_arg`` in
  14 functions with variable argument lists either must be compatible with
  15 that of the actual argument, or that one type must be a pointer to
  16 ``void`` and the other a pointer to a character type.  GNU C
  17 implements the POSIX XSI extension that additionally permits the use
  18 of ``va_arg`` with a pointer type to receive arguments of any other
  19 pointer type.
  20
  21 In particular, in GNU C :samp:`va_arg (ap, void *)` can safely be used
  22 to consume an argument of any pointer type.