Function c_str

test/doctest.h:642–642

the only functions I'm willing to leave in the interface - available for inlining

    // the only functions I'm willing to leave in the interface - available for inlining
    const char* c_str() const { return const_cast<String*>(this)->c_str(); } // NOLINT
    char*       c_str() {
        if (isOnStack()) {
            return reinterpret_cast<char*>(buf);