c++ - Enum to string : return the enum integer value if invalid / not found

Question

So, I implemented an enumToString function for several enums that I use a lot (often asked in SO: Is there a simple way to convert C++ enum to string?, Easy way to use variables of enum types as string in C?, ...). This makes the error messages WAY easier to debug, but I have to maintain the function to add the values that have no string description sometimes.

My code looks like this:

typedef std::map<my_enum_e, const char *> enum_map_t;
static bool s_enum_map_initialized = false;

static enum_map_t s_enum_strings;

static void s_init_maps()
{
#define ADD_ENUM( X ) s_enum_strings[X] = #X;

    if( s_enum_strings.size() == 0)
    {
        ADD_CLASS( MY_ENUM_1 );
        ADD_CLASS( MY_ENUM_2 );
        /* ... all enums */
    }
    s_enum_map_initialized = true;
}

const char *Tools::enumCString( my_enum_e e )
{
    if( ! s_enum_map_initialized )
    {
        s_init_maps();
    }

    // todo: use the iterator instead of searching twice
    if( s_enum_strings.find(e) != s_enum_strings.end() )
    {
        return s_class_strings[e];
    }

    return "(unknown enum_e)";
}

Now, what I want, is that when I don't find the enum in the map, to return "(unknown enum %d)", e . Which will give me the value of the enum I missed.

This way, even if I didn't add it to the map, I still have its value and I can debug my program.

I can't find a way to do that simply: a stringstream instanciated on the stack will be destroyed right after the return, a static stringstream is not thread-safe, ...

edit: of course, using a std::string as return type would allow me to format it, but I call these functions very often in my code, I figured passing a const char * pointer is faster, since I don't have to push the std::string onto the stack each time.

Any solution?

Answer 1

Return a std::string rather than a char*.

This would allow you to use a std::stringstream to generate your message. The calling site would then just have to use the .c_str( ) member function on std::string to get the C-style pointer (if required).