CODEWITHSUNDEEP
c++iteratorstdmap
avinashse
avinashse

Reputation: 1460

Fetch first two elements from map

I have to read only the first two elements from an std::map.

Here's my code:

#include<iostream>
#include<map>
#include<iterator>
using namespace std;
int main() {
    map<int,int> a;
    map<int,int>:: iterator itr;
    itr = a.begin();
    cout<<itr->first<<" "<<itr->second<<endl;
    next(itr);
    cout<<itr->first<<" "<<itr->second<<endl;
    return 0;
}

I'm getting this error:

next was not declared in the scope

what am I missing here and if there is a better way to do it?

Upvotes: 0

Views: 311

Answers (2)

Ankit Mishra
Ankit Mishra

Reputation: 590

you should use itr++ to move itr forward to point next set of pairs. and you can access them by map->first; and map->second;

Upvotes: 0

Azeem
Azeem

Reputation: 14637

For using std::next, you need to have at least C++11 compliant compiler.

std::next returns a new incremented iterator. So, you need to use its return value to get the incremented iterator i.e.:

itr = next( itr );

Right now, itr is pointing to the same element because the return value is not used.

If you meant to increment the itr without a new iterator then std::advance is a better candidate here i.e.:

std::advance( itr, 1 );

If you're using a pre-C++11 compiler then you can use increment operator like this:

itr++;

Or,

++itr;

Here's a live demo.

In addition, the map is uninitialized/empty and you're trying to access its elements that are not there and this would result in Undefined Behavior.

Relevant read:

Upvotes: 2

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