Using char* as a key in std::map

Question

I am trying to figure out why the following code is not working, and I am assuming it is an issue with using char* as the key type, however I am not sure how I can resolve it or why it is occuring. All of the other functions I use (in the HL2 SDK) use char* so using std::string is going to cause a lot of unnecessary complications.

std::map<char*, int> g_PlayerNames;  int PlayerManager::CreateFakePlayer() {     FakePlayer *player = new FakePlayer();     int index = g_FakePlayers.AddToTail(player);      bool foundName = false;      // Iterate through Player Names and find an Unused one     for(std::map<char*,int>::iterator it = g_PlayerNames.begin(); it != g_PlayerNames.end(); ++it)     {         if(it->second == NAME_AVAILABLE)         {             // We found an Available Name. Mark as Unavailable and move it to the end of the list             foundName = true;             g_FakePlayers.Element(index)->name = it->first;              g_PlayerNames.insert(std::pair<char*, int>(it->first, NAME_UNAVAILABLE));             g_PlayerNames.erase(it); // Remove name since we added it to the end of the list              break;         }     }      // If we can't find a usable name, just user 'player'     if(!foundName)     {         g_FakePlayers.Element(index)->name = "player";     }      g_FakePlayers.Element(index)->connectTime = time(NULL);     g_FakePlayers.Element(index)->score = 0;      return index; } 

Answer 1

You need to give a comparison functor to the map otherwise it's comparing the pointer, not the null-terminated string it points to. In general, this is the case anytime you want your map key to be a pointer.

For example:

struct cmp_str {    bool operator()(char const *a, char const *b) const    {       return std::strcmp(a, b) < 0;    } };  map<char *, int, cmp_str> BlahBlah; 

Answer 2

You can't use char* unless you are absolutely 100% sure you are going to access the map with the exact same pointers, not strings.

Example:

char *s1; // pointing to a string "hello" stored memory location #12 char *s2; // pointing to a string "hello" stored memory location #20 

If you access map with s1 you will get a different location than accessing it with s2.