Boost :: filesystem :: path and std :: string

Question

I have a String class that has a member of std :: string. One of the designers

String (std::string s)
{
    // member: std::string _mString;
    _mString = s;  // error on path assignment
}

Now I have functions that take a String parameter as a parameter, for example. Load (String path);

but it turns out that boost :: filesystem :: path :: string () is incompatible with this String constructor, but usually assign ok

boost::filesystem::path somepath("some directory")
std::string filename = somepath.extension(); // OK!

What's happening? How can I make my constructor work? Thank.

EDIT: The problem is resolved by making it const ref, but still curious why the error is because it seems acceptable to pass a copy because it can be assigned directly. Error in xstring file

void __CLR_OR_THIS_CALL _Tidy(bool _Built = false,
        size_type _Newsize = 0)
        {   // initialize buffer, deallocating any storage
        if (!_Built)
            ;
        else if (_BUF_SIZE <= _Myres)
            {   // copy any leftovers to small buffer and deallocate
            _Elem *_Ptr = _Bx._Ptr;
            if (0 < _Newsize)
                _Traits_helper::copy_s<_Traits>(_Bx._Buf, _BUF_SIZE, _Ptr, _Newsize);
            _Mybase::_Alval.deallocate(_Ptr, _Myres + 1);
            }
        _Myres = _BUF_SIZE - 1; // **** ERROR ***
        _Eos(_Newsize);
        }

Answer 1

: String (std::string s) String (const std::string& s)