I want to create something like a python dictionary in C++

Question

I'm using a struct. Is there some way to iterate through all the items of type "number"?

struct number { int value; string name; };

I'm not sure the question. In C++ we have "maps", i.e. `std::map` and `std::unordered_map`. [See here](http://en.cppreference.com/w/cpp/container) for a list of standard data structures. — Jesse Good, Jan 30 '16 at 02:17
If you want to create a python-like dictionary, then you want to implement a [hashmap](http://stackoverflow.com/questions/327311/how-are-pythons-built-in-dictionaries-implemented). So look into `std::map` and `std::unordered_map` as suggested both in the comments and answers sections. C++ implementation example [here](http://stackoverflow.com/questions/3578083/what-is-the-best-way-to-use-a-hashmap-in-c). — Reti43, Jan 30 '16 at 02:32

score 10 · Answer 1 · answered Jan 30 '16 at 03:20

In c++ map works like python dictionary, But there is a basic difference in two languages. C++ is typed and python having duck typing. C++ Map is typed and it can't accept any type of (key, value) like python dictionary. A sample code to make it more clear -

  map<int, char> mymap;
  mymap[1] = 'a';
  mymap[4] = 'b';
  cout<<"my map is -"<<mymap[1]<<" "<<mymap[4]<<endl;

You can use tricks to have a map which will accept any type of key, Refer - http://www.cplusplus.com/forum/general/14982/

score 3 · Answer 2 · answered Jan 30 '16 at 02:25

As per my understanding you want to access a value and name using number. You can go for array of structure like number n[5]; where n[0],n[1],...n[4] but we have some additional features in c++ to achieve this with the predefined map, set You can find lots of examples for map

score 3 · Answer 3 · answered Jan 30 '16 at 03:54

You can use std::map (or unordered_map)

     //  Key  Value Types.
std::map<int, std::string> data {{1, "Test"}, {2, "Plop"}, {3, "Kill"}, {4, "Beep"}};

for(auto item: data) {
                 // Key                  Value
    std::cout << item.first << " : " << item.second << "\n";
}

Compile and run:

> g++ -std=c++14 test.cpp
> ./a.out
1 : Test
2 : Plop
3 : Kill
4 : Beep

The difference between std::map and std::unordered_map is for std::map the items are ordered by the Key while in std::unordered_map the values are not ordered (thus they will be printed in a seemingly random order).

Internally they use very different structures but I am sure you are not interested in that level of detail.

I want to create something like a python dictionary in C++

3 Answers3