This is plain in C++ 17. Use std::map + std::any + std::any_cast: #include <map> #include <string> #include <any> int main() { std::map<std::string, std::any> notebook; std::string name{ “Pluto” }; int year = 2015; notebook[“PetName”] = name; notebook[“Born”] = year; std::string name2 = std::any_cast<std::string>(notebook[“PetName”]); // = “Pluto” int year2 = std::any_cast<int>(notebook[“Born”]); // = 2015 }
You are using a const char * as a lookup key for find(). For the map containing const char* this is the correct type that find expects and the lookup can be done directly. The map containing std::string expects the parameter of find() to be a std::string, so in this case the const char* first … Read more
std::map<X, Y>: is an ordered structure with respect to keys (that is, when you iterate over it, keys will be always increasing). supports unique keys (Xs) only offers fast find() method (O(log n)) which finds the Key-Value pair by Key offers an indexing operator map[key], which is also fast std::list<std::pair<X, Y> >: is a simple … Read more
Use std::pair<int32,int32> for the key: std::map<std::pair<int,int>, int> myMap; myMap[std::make_pair(10,20)] = 25; std::cout << myMap[std::make_pair(10,20)] << std::endl;
They way I understand it, references are implemented as pointers under the hood. The reason why you can’t store them in a map is purely semantic; you have to initialize a reference when it’s created and you can’t change it afterward anymore. This doesn’t mesh with the way a map works.
C++11 allows you to do: for (const auto& kv : myMap) { std::cout << kv.first << ” has value ” << kv.second << std::endl; } C++17 allows you to do: for (const auto& [key, value] : myMap) { std::cout << key << ” has value ” << value << std::endl; } using structured binding. UPDATE: … Read more
Your main problem is that you are calling a method called first() in the iterator. What you are meant to do is use the property called first: …append(iter->first) rather than …append(iter->first()) As a matter of style, you shouldn’t be using new to create that string. std::string something::toString() { std::map<std::string, std::string>::iterator iter; std::string strToReturn; //This is … Read more
Contrary to most existing answers here, note that there are actually 4 methods related to finding an element in a map (ignoring lower_bound, upper_bound and equal_range, which are less precise): operator[] only exist in non-const version, as noted it will create the element if it does not exist at(), introduced in C++11, returns a reference … Read more
If you have a C++11-compliant compiler, here’s an easy way to do this: std::map<K, V>::iterator itr = myMap.begin(); while (itr != myMap.end()) { if (ShouldDelete(*itr)) { itr = myMap.erase(itr); } else { ++itr; } } The idea is to walk the iterator forward from the start of the container to the end, checking at each … Read more
Since a map can only have at most one key, count will essentially stop after one element has been found. However, in view of more general containers such as multimaps and multisets, find is strictly better if you only care whether some element with this key exists, since it can really stop once the first … Read more