Initialize a std::pair in C++

This post will discuss how to initialize a std::pair in C++.

1. Initialization Constructor

A simple solution to create a std::pair is using its initialization constructor, which takes two arguments corresponding to the first and second member of the pair respectively.

#include <iostream>

#include <utility>

int main()

{

std::pair <std::string, int> p("John", 25);

std::cout << "The pair is (" << p.first << ", " << p.second << ")\n";

return 0;

}

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Output:

The pair is (John, 25)

2. Using `std::make_pair`

Another common solution to construct a pair object is using the std::make_pair function, that takes two arguments corresponding to the first and second member of the pair respectively. The advantage of this method is that std::pair template types can be implicitly deduced from its arguments.

#include <iostream>

#include <utility>

int main()

{

std::pair <std::string, int> p = std::make_pair("John", 25);

std::cout << "The pair is (" << p.first << ", " << p.second << ")\n";

return 0;

}

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Output:

The pair is (John, 25)

3. Using Aggregate Initialization

Starting with C++11, you can also initialize a pair from the braced-init-list.

#include <iostream>

#include <utility>

int main()

{

std::pair <std::string, int> p = {"John", 25};

std::cout << "The pair is (" << p.first << ", " << p.second << ")\n";

return 0;

}

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Output:

The pair is (John, 25)

The following code is the same as above, but uses the direct-list-initialization syntax:

#include <iostream>

#include <utility>

int main()

{

std::pair <std::string, int> p {"John", 25};

std::cout << "The pair is (" << p.first << ", " << p.second << ")\n";

return 0;

}

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Output:

The pair is (John, 25)

4. Copy Constructor

Finally, you can use a copy constructor to initialize a pair object with corresponding members of another pair object.

#include <iostream>

#include <utility>

int main()

{

std::pair <std::string, int> p({"John", 25});

std::cout << "The pair is (" << p.first << ", " << p.second << ")\n";

return 0;

}

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Output:

The pair is (John, 25)

That’s all about initializing a std::pair in C++.

Initialize a std::pair in C++

1. Initialization Constructor

2. Using std::make_pair

3. Using Aggregate Initialization

4. Copy Constructor

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2. Using `std::make_pair`