C++ – Use of for_each on map elements


I have a map where I'd like to perform a call on every data type object member function. I yet know how to do this on any sequence but, is it possible to do it on an associative container?

The closest answer I could find was this: Boost.Bind to access std::map elements in std::for_each. But I cannot use boost in my project so, is there an STL alternative that I'm missing to boost::bind?

If not possible, I thought on creating a temporary sequence for pointers to the data objects and then, call for_each on it, something like this:

class MyClass
 void Method() const;

std::map<int, MyClass> Map;

std::vector<MyClass*> Vector;
std::transform(Map.begin(), Map.end(), std::back_inserter(Vector), std::mem_fun_ref(&std::map<int, MyClass>::value_type::second));
std::for_each(Vector.begin(), Vector.end(), std::mem_fun(&MyClass::Method));

It looks too obfuscated and I don't really like it. Any suggestions?

Best Answer

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.


const auto is safer if you don't want to modify the map.