gcc/doc/cpp/macros.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 .. _macros:
   7
   8 Macros
   9 ------
  10
  11 A :dfn:`macro` is a fragment of code which has been given a name.
  12 Whenever the name is used, it is replaced by the contents of the macro.
  13 There are two kinds of macros.  They differ mostly in what they look
  14 like when they are used.  :dfn:`Object-like` macros resemble data objects
  15 when used, :dfn:`function-like` macros resemble function calls.
  16
  17 You may define any valid identifier as a macro, even if it is a C
  18 keyword.  The preprocessor does not know anything about keywords.  This
  19 can be useful if you wish to hide a keyword such as ``const`` from an
  20 older compiler that does not understand it.  However, the preprocessor
  21 operator ``defined`` (see :ref:`defined`) can never be defined as a
  22 macro, and C++'s named operators (see :ref:`c++-named-operators`) cannot be
  23 macros when you are compiling C++.
  24
  25 .. toctree::
  26   :maxdepth: 2
  27
  28   macros/object-like-macros
  29   macros/function-like-macros
  30   macros/macro-arguments
  31   macros/stringizing
  32   macros/concatenation
  33   macros/variadic-macros
  34   macros/predefined-macros
  35   macros/undefining-and-redefining-macros
  36   macros/directives-within-macro-arguments
  37   macros/macro-pitfalls