std::pair::pair

(1) default constructor

Constructs a pair object with its elements value-initialized.

(2) copy / move constructor (and implicit conversion)

The object is initialized with the contents of the pr pair object.
The corresponding member of pr is passed to the constructor of each of its members.

(3) initialization constructor

Member first is constructed with a and member second with b.

(4) piecewise constructor

Constructs members first and second in place, passing the elements of first_args as arguments to the constructor of first, and the elements of second_args to the constructor of second.

Parameters

pr

Another pair object.
This may be an object of the same type as the object being constructed or of a pair type whose elements' types are implicitly convertible to those in the pair being constructed.

a

An object of the type of first, or some other type implicitly convertible to it.

b

An object of the type of second, or some other type implicitly convertible to it.

pwc

The piecewise_construct object.
The only purpose of this argument is to select the proper constructor signature. It conveys no information to be incorporated into the new object.

first_args, second_args

tuple objects with the arguments to be passed to the constructors of members first and second.

Example

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// pair::pair example
#include <utility>      // std::pair, std::make_pair
#include <string>       // std::string
#include <iostream>     // std::cout
int main () {
  std::pair <std::string,double> product1;                     // default constructor
  std::pair <std::string,double> product2 ("tomatoes",2.30);   // value init
  std::pair <std::string,double> product3 (product2);          // copy constructor
  product1 = std::make_pair(std::string("lightbulbs"),0.99);   // using make_pair (move)
  product2.first = "shoes";                  // the type of first is string
  product2.second = 39.90;                   // the type of second is double
  std::cout << "The price of " << product1.first << " is $" << product1.second << '\n';
  std::cout << "The price of " << product2.first << " is $" << product2.second << '\n';
  std::cout << "The price of " << product3.first << " is $" << product3.second << '\n';
  return 0;
}

The price of lightbulbs is $0.99
The price of shoes is $39.9
The price of tomatoes is $2.3

Data races

Exception safety

See also

pair::operator=

Assign contents (public member function)

make_pair

Construct pair object (function template)

tuple

Tuple (class template)