BOOST_PP_EXPAND

The BOOST_PP_EXPAND macro performs a double macro-expansion on its argument.

Usage

BOOST_PP_EXPAND (x)

Arguments

x The argument to be expanded twice.

Remarks

This macro is useful when a delay is necessary to produce the correct semantics of a macro invocation. For example, when a macro expands to an argument list to another macro. This macro will expand the argument list on the first pass, and then rescan to expand any more macros.

Requirements

Header: <boost/preprocessor/facilities/expand.hpp>

Sample Code

#include <[boost/preprocessor/control/if.hpp](../headers/control/if.html)>
#include <[boost/preprocessor/facilities/expand.hpp](../headers/facilities/expand.html)>

#define MACRO(a, b, c) (a)(b)(c)
#define ARGS() (1, 2, 3)[BOOST\_PP\_EXPAND](expand.html)(MACRO ARGS()) // expands to (1)(2)(3)

#define SAMPLE(n) \[BOOST\_PP\_EXPAND](expand.html)( \
      MACRO \[BOOST\_PP\_IF](if.html)( \
         n, \
         (x, y, z), \
         (a, b, c) \
      ) \
   ) \
   /**/

SAMPLE(0) // expands to (a)(b)(c)
SAMPLE(1) // expands to (x)(y)(z)

Copyright Housemarque Oy 2002 Copyright Paul Mensonides 2002

Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at www.boost.org/LICENSE_1_0.txt)