CODEWITHSUNDEEP
c++
Rahul
Rahul

Reputation: 277

Implement Vector of Map in c++

I want to use vector of Map in c++. I have list of mapped values, which I want to store as map in vector. My requirement goes something like this: 1. For N columns, I have a map of values . 2. I want to maintain map of for each i in N.

I am trying to maintain this in Vector >. Please let me know how to make it work.

I am using following code to add mappings

void fun() 
{
vector< map < string, int> > myVect;
myVect.push_back(new map< string, int> );
myVect.push_back(new map< string, int> );

map< string, int> entry1 = myVect[0];

entry1["ABC"] = 1;
entry1["DEF"] = 2;

map< string, int> entry2 = myVect[1];

entry1["ABC"] = 5;
entry1["RKD"] = 9;
}

Why doesn't work ?

Upvotes: 6

Views: 22459

Answers (2)

David
David

Reputation: 28178

Justin answered the big part of it but another issue is:

map< string, int> entry1 = myVect[0];

This will copy the map from your vector. You probably want a reference instead:

map< string, int>& entry1 = myVect[0];

Upvotes: 5

justin
justin

Reputation: 104698

In your example, you are pushing back using a pointer (via new), and not by const reference or value. Your 'vector of maps' declaration is fine, but the insertion is causing a compiler error.

To push a map into the vector, use the form:

std::map<std::string,int> m;
// populate m if needed
x.push_back(m);

or simply

x.push_back(std::map<std::string,int>());

if you want to push an empty map.

Note that new is not needed here.

Upvotes: 12

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