How to write 3d mapping in C++?

Question

Can you please tell me how I can write multidimensional map. For two dimensional map, I did the following:

map<string, int> Employees
Employees[“person1”] = 200;

I was trying to use something similar to following for 3d mapping.

map<string, string, int> Employees;
Employees[“person1”, “age”] = 200;

Can you please tell me the correct way to do this?

and Is there a way I can initialize all the map elements to be 0 ? Just like on a array we can say int array[10]={0};

score 9 · Accepted Answer · answered Feb 12 '12 at 10:06

9

You need to create map of maps like that.

map<string, map<string, int> > employees;
employees["person1"]["age"] = 200;

answered Feb 12 '12 at 10:06

Boris Strandjev

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Is there a way I can initialize all the map function to be 0 ? Just like on a array we can say `int array[10]={0};` – Learner_51 Feb 12 '12 at 10:25
The call to map[key] initializes the object with the type default constructor. For integer this is exactly zero. This means that for any two randomly chosen keys `emplyees["foo"]["bar"] == 0` will return true. – Boris Strandjev Feb 12 '12 at 10:27
Ok, I should have tried it out first. Thanks for all the help. – Learner_51 Feb 12 '12 at 10:29

score 6 · Answer 2 · answered Feb 12 '12 at 10:14

6

You can use the pair class of the utility library to combine two objects:

map<pair<string, string>, int> Employees;
Employees[make_pair("person1", "age")] = 200;

See http://www.cplusplus.com/reference/std/utility/pair/

answered Feb 12 '12 at 10:14

Eser Aygün

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eudoxos · Answer 3 · 2012-02-12T10:21:56.423

3

Instead of nested map, you can use tuple as keys; (this is a c++11 code, you could do the same with boost::tuple as well).

#include<map>
#include<tuple>
#include<string>
using namespace std;
map<tuple<string,string>,int> m;
int main(){
    m[make_tuple("person1","age")]=33;
}

edited Feb 12 '12 at 10:21

answered Feb 12 '12 at 10:16

eudoxos

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score 0 · Answer 4 · edited May 23 '17 at 10:27

0

what you are doing here is not 3D mapping but 2D mapping, how to use stl::map as two dimension array

Correct 3D mapping will be like

map<string, map<string, map<int, string> > > Employees;
Employees[“person1”][“age”][20] = "26/10/2014";

edited May 23 '17 at 10:27

Community

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answered Oct 26 '14 at 09:13

Ritwik

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How to write 3d mapping in C++?

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