convert/doc/06_algorithms.qbk

[section:convert_algorithms Boost.Convert with Standard Algorithms]

The following code demonstrates a failed attempt to convert a few strings with ['boost::lexical_cast]:

 array<char const*, 5> strings = {{ "0XF", "0X10", "0X11", "0X12", "not int" }};
 std::vector<int>     integers;

 try
 {
    std::transform(
        strings.begin(),
        strings.end(),
        std::back_inserter(integers),
        boost::bind(boost::lexical_cast<int, std::string>, _1));

        BOOST_ASSERT(!"We should not be here");
 }
 catch (std::exception&)
 {
    // No strings converted.
 }

The first take by ['boost::convert] is more successful but still not quite satisfactory (your mileage may vary) as conversion is interrupted when ['boost::convert] comes across an invalid input:

 boost::array<char const*, 5> strings = {{ "0XF", "0X10", "0X11", "0X12", "not int" }};
 std::vector<int>            integers;
 boost::cstringstream_converter   cnv; // stringstream-based char converter

 try
 {
   std::transform(
        strings.begin(),
        strings.end(),
        std::back_inserter(integers),
        convert<int>::from<string>(cnv(std::hex)));

        BOOST_ASSERT(!"We should not be here");
 }
 catch (std::exception&)
 {
    // Only the first four strings converted. Failed to convert the last one.

    BOOST_ASSERT(integers[0] == 15);
    BOOST_ASSERT(integers[1] == 16);
    BOOST_ASSERT(integers[2] == 17);
    BOOST_ASSERT(integers[3] == 18);
 }

And at last a fully working version (with a conversion-failure fallback value provided):

 boost::array<char const*, 5> strings = {{ "0XF", "0X10", "0X11", "0X12", "not int" }};
 std::vector<int>            integers;
 boost::cstringstream_converter   cnv; // stringstream-based char converter

 std::transform(
    strings.begin(),
    strings.end(),
    std::back_inserter(integers),
    convert<int>::from<string>(ccnv(std::hex)).value_or(-1));

 BOOST_ASSERT(integers[0] == 15);
 BOOST_ASSERT(integers[1] == 16);
 BOOST_ASSERT(integers[2] == 17);
 BOOST_ASSERT(integers[3] == 18);
 BOOST_ASSERT(integers[4] == -1); // Failed conversion

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