Boost::filesystem, std::sort: trouble retaining information on sort passes

Question

I\'m trying to use std::sort on a data type that contains information read from a boost::filesystem::dictionary_iterator. It appears that as the sortin

Answer 1

The call to compare() at the end is wrong, it returns an int that can be -1, 0 or 1 like strcmp(). Use a simple call to std::less()(a_filename, b_filename) instead. Also make sure you have unit tests that make sure the comparator creates a strict-weak ordering, as is required for std::sort.

Comparator with internal checking:

inline bool do_compare(const File& a, const File& b)
{
    /* ... */
} 

bool compare(const File& a, const File& b)
{
    bool const res = do_compare(a, b);
    if(res)
        assert(!do_compare(b, a));
    return res;
}

If NDEBUG is defined (i.e. assert() deactivated) the compiler should be able to optimize this to the same amount of code as before. And now, I wish you much fun writing the code that sorts the filenames 9.png, 10.png and 11.png in that order. ;)