std::transform and move semantics

Question

I\'m using Boost.Filesystem to create a listing of files in a directory. I use boost::filesystem::recursive_directory_iterator and std::copy to put eac

Answer 1

This looks like a job for make_move_iterator:

std::transform(make_move_iterator(buffer.begin()),
                make_move_iterator(buffer.end()), buffer_native.begin(),
                [](boost::filesystem::directory_entry&& de) -> std::string
{
    // still makes copy :/ perhaps native() would work better, I don't know
    std::string temp = de.path().string();
    temp += "\n";

    return temp;
}

A move iterator is simply an iterator which moves its dereference result. Note that the class needs to support move semantics for this to even make a difference; I don't know if Boost FS does.

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Note if your goal is to output them on separate lines, you're doing it wrong. Formatted printing shouldn't require the input data be in a certain format, that defeats the purpose. Adding newlines to your data just to format it to have newlines is nasty. It's handled for you by ostream_iterator anyway:

std::copy(buffer.begin(), buffer.end(), //               vvvv
            std::ostream_iterator<std::string>(out_file, "\n"));

Anything more complex, make a lambda in for printing; don't modify your data beforehand.