Geek asks and answers

What are the costs of increasing the identifier: lexical_cast?

For a function such as:

template< typename T >
void function1( const T &t )
{
  function2( boost::lexical_cast<std::string>(t) );
}

What overhead occurs if the type passed in function1is already std::string?

Depending on the type I'm lexical_cast-ing on?

Is it wrong to do an overloaded function to bypass the casting? For instance:.

void function1( const std::string &t )
{
  function2( t );
}

template< typename T >
void function1( const T &t )
{
  function1( boost::lexical_cast<std::string>(t) );
}

The boost version may be relevant to your answer, as I understand that I lexical_castreceived several optimizations in the versions.

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2 answers

, lexical_cast (1.51.0) , " ", . , , " " .

(boost/lexical_cast.hpp:2268):

template <typename Target, typename Source>
Target lexical_cast(const Source &arg)
{
    static if( is_character_type_to_character_type<Target, src> ||
               is_char_array_to_stdstring<Target, src> ||
               is_same_and_stdstring<Target, src> )
    //         ^-- optimization for std::string to std::string and similar stuff
    {
      return arg;
    }
    else
    {
      /* some complicated stuff */
    }
}

- , , lexical_cast_do_cast "", .: (

+4

http://www.boost.org/doc/libs/1_51_0/doc/html/boost_lexical_cast/performance.html

, .

10000 :

    typedef BOOST_DEDUCED_TYPENAME ::boost::type_traits::ice_or<
            ::boost::detail::is_xchar_to_xchar<Target, src >::value,
            ::boost::detail::is_char_array_to_stdstring<Target, src >::value,
            ::boost::type_traits::ice_and<
                 ::boost::is_same<Target, src >::value,
                 ::boost::detail::is_stdstring<Target >::value
            >::value
    > shall_we_copy_t;

shall_we_copy_t::value , 3- (Target src), Target type std::basic_string).

    typedef BOOST_DEDUCED_TYPENAME ::boost::mpl::if_c<
        shall_we_copy_t::value,
        ::boost::detail::lexical_cast_copy<src >,
        BOOST_DEDUCED_TYPENAME ::boost::mpl::if_c<
             shall_we_copy_with_dynamic_check_t::value,
             ::boost::detail::lexical_cast_dynamic_num<Target, src >,
             ::boost::detail::lexical_cast_do_cast<Target, src >
        >::type
    >::type caster_type;

shall_we_copy_t::value , caster_type lexical_cast_copy

return caster_type::lexical_cast_impl(arg);

, lexical_cast_copy::lexical_cast_impl,

    template <typename Source>
    struct lexical_cast_copy
    {
        static inline Source lexical_cast_impl(const Source &arg)
        {
            return arg;
        }
    };
+1

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