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c++c++11c++17stdvectorstd-pair

How to update recently entered element in std::vector<pair<int, int>>?

How can one update the value for pairs in any vector class of pair type?

Example : 

V.push_back(make_pair(1, 3));

If I wish to update 3 to say 5 or something, how do I achieve that?

Solution

  • Assuming that you want to update the last std::pair input just after inserting to the std::vector<std::pair<int, int>>.

    In you can make use of second overload of std::vector::emplace_back, which returns a reference to the element inserted:

    #include <vector>

std::vector<std::pair<int, int>> vec;
auto &pair = vec.emplace_back(1, 3); // construct in-place and get the reference to the inserted element
pair.second = 5;                     // change the value directly like this

    Update:

    In , the same can be achieved by the std::vector::insert member, which returns iterator pointing to the inserted element.

    #include <vector>

std::vector<std::pair<int, int>> vec;
// insert the element to vec and get the iterator pointing to the element
const auto iter = vec.insert(vec.cend(), { 1, 3 });
iter->second = 5; // change the value