out_value.rst.svn-base

本人找过多个在linux下c++的lua5.1封装库,但很少.luabind已经release的版本只支持lua5.0.这个版本是我从其cvs(svc)上取出的并支持最新的lua5.1.强烈推荐.

out_value
----------------

Motivation
~~~~~~~~~~

This policy makes it possible to wrap functions that take non-const references
or pointer to non-const as it's parameters with the intention to write return 
values to them. Since it's impossible to pass references to primitive types
in lua, this policy will add another return value with the value after the
call. If the function already has one return value, one instance of this
policy will add another return value (read about multiple return values in
the lua manual).

Defined in
~~~~~~~~~~

.. parsed-literal::

    #include <luabind/out_value_policy.hpp>

Synopsis
~~~~~~~~

.. parsed-literal::

    out_value(index, policies = none)


Parameters
~~~~~~~~~~

=============== =============================================================
Parameter       Purpose
=============== =============================================================
``index``       The index of the parameter to be used as an out parameter.
``policies``    The policies used internally to convert the out parameter
                to/from Lua. ``_1`` means **to** C++, ``_2`` means **from**
                C++.
=============== =============================================================

Example
~~~~~~~

.. parsed-literal::

    void f1(float& val) { val = val + 10.f; }
    void f2(float\* val) { \*val = \*val + 10.f; }

    module(L)
    [
        def("f", &f, **out_value(_1)**)
    ];

    Lua 5.0  Copyright (C) 1994-2003 Tecgraf, PUC-Rio
    > print(f1(10))
    20
    > print(f2(10))
    20