How do I write a map literal in C++11?

c++ c++11 map literals
abw333 picture abw333 · Nov 27, 2013 · Viewed 16.8k times · Source

In Python, I can write a map literal like this:

mymap = {"one" : 1, "two" : 2, "three" : 3}

How can I do the equivalent in C++11?

Answer

aaronman picture aaronman · Nov 27, 2013

You can actually do this: 

std::map<std::string, int> mymap = {{"one", 1}, {"two", 2}, {"three", 3}};

What is actually happening here is that std::map stores an std::pair of the key value types, in this case std::pair<const std::string,int>. This is only possible because of c++11's new uniform initialization syntax which in this case calls a constructor overload of std::pair<const std::string,int>. In this case std::map has a constructor with an std::intializer_list which is responsible for the outside braces.

So unlike python's any class you create can use this syntax to initialize itself as long as you create a constructor that takes an initializer list (or uniform initialization syntax is applicable)

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