Insert a pair to a vector in C++

This post will discuss how to add a std::pair to a vector of pairs in C++.

1. Using `std::emplace_back` function

The standard solution to add a new std::pair to a vector of pairs is using the std::emplace_back(T&&... args) function, which in-place construct and insert a pair at the end of a vector, using the specified arguments for its constructor. Note that this function is added in C++11.

Its usage is demonstrated below:

#include <iostream>

#include <vector>

#include <utility>

int main()

{

std::vector<std::pair<int, int>> pairs = {{1, 2}, {3, 4}, {5, 6}};

// add a new pair to vector using emplace_back()

pairs.emplace_back(7, 8);

// print all pairs

for (auto p: pairs) {

std::cout << "(" << p.first << ", " << p.second << ") ";

}

return 0;

}

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Output:

(1, 2) (3, 4) (5, 6) (7, 8)

2. Using `std::push_back` function

Another simple solution is to add a new std::pair to a vector of pairs is using the std::push_back(T&& val) function, which either copies (or moves) a pair into the vector. A pair can be constructed in several ways:

⮚ Using std::make_pair function

#include <iostream>

#include <vector>

#include <utility>

int main()

{

std::vector<std::pair<int, int>> pairs = {{1, 2}, {3, 4}, {5, 6}};

// add a new pair to vector using make_pair()

pairs.push_back(std::make_pair(7, 8));

// print all pairs

for (auto p: pairs) {

std::cout << "(" << p.first << ", " << p.second << ") ";

}

return 0;

}

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Output:

(1, 2) (3, 4) (5, 6) (7, 8)

⮚ Using Aggregate Initialization

#include <iostream>

#include <vector>

#include <utility>

int main()

{

std::vector<std::pair<int, int>> pairs = {{1, 2}, {3, 4}, {5, 6}};

// add a new pair to vector using aggregate initialization

pairs.push_back({7, 8});

// print all pairs

for (auto p: pairs) {

std::cout << "(" << p.first << ", " << p.second << ") ";

}

return 0;

}

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Output:

(1, 2) (3, 4) (5, 6) (7, 8)

⮚ Using Initialization Constructor

#include <iostream>

#include <vector>

#include <utility>

int main()

{

std::vector<std::pair<int, int>> pairs = {{1, 2}, {3, 4}, {5, 6}};

// add a new pair to vector using constructor

pairs.push_back(std::pair<int, int>(7, 8));

// print all pairs

for (auto p: pairs) {

std::cout << "(" << p.first << ", " << p.second << ") ";

}

return 0;

}

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Output:

(1, 2) (3, 4) (5, 6) (7, 8)

That’s all about adding a new std::pair to a vector of pairs in C++.

Insert a pair to a vector in C++

1. Using std::emplace_back function

2. Using std::push_back function

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1. Using `std::emplace_back` function

2. Using `std::push_back` function