Method operator-

src/fl/stl/basic_string.h:84–84

        iterator operator+(difference_type n) const FL_NOEXCEPT { return iterator(ptr + n); }
        iterator operator-(difference_type n) const FL_NOEXCEPT { return iterator(ptr - n); }
        iterator& operator+=(difference_type n) FL_NOEXCEPT { ptr += n; return *this; }
        iterator& operator-=(difference_type n) FL_NOEXCEPT { ptr -= n; return *this; }
        difference_type operator-(const iterator& other) const FL_NOEXCEPT { return ptr - other.ptr; }