class template

std::pair

<utility>
template <class T1, class T2> struct pair;
Pair of values
This class couples together a pair of values, which may be of different types (T1 and T2). The individual values can be accessed through the public members first and second.

The class is defined as:

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template <class T1, class T2> struct pair
{
  typedef T1 first_type;
  typedef T2 second_type;

  T1 first;
  T2 second;
  pair() : first(T1()), second(T2()) {}
  pair(const T1& x, const T2& y) : first(x), second(y) {}
  template <class U, class V>
    pair (const pair<U,V> &p) : first(p.first), second(p.second) { }
}


Members

first_type, second_type
Alises of template parameters T1 and T2 respectively.
first, second
Data members containing the first and second values stored in the pair.
pair()
Constructs a pair object with each of its members first and second constructed with their respective default constructors.
pair(const T1& x, const T2& y)
Constructs a pair object with its members first and second initialized to x and y, respectively.
template <class U, class V> pair (const pair<U,V> &p)
Constructs a pair object with its members first and second initialized to the corresponding elements in p, which must be of any couple of implicitly-convertible types (including the same types).

Global operators

The header <utility> also overloads the relational operators ==, <, !=, >, >= and <= , so as to be able to compare pair objects of the same type directly:

Two pair objects are compared equal if the first elements in both objects compare equal to each other and both second elements also compare equal to each other - they all have to match.

In inequality comparisons (<, >), the first elements are compared first, and only if the inequality comparison is not true for them, the second elements are compared.

Example

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#include <iostream>
#include <utility>
#include <string>
using namespace std;

int main () {
  pair <string,double> product1 ("tomatoes",3.25);
  pair <string,double> product2;
  pair <string,double> product3;

  product2.first = "lightbulbs";     // type of first is string
  product2.second = 0.99;            // type of second is double

  product3 = make_pair ("shoes",20.0);

  cout << "The price of " << product1.first << " is $" << product1.second << "\n";
  cout << "The price of " << product2.first << " is $" << product2.second << "\n";
  cout << "The price of " << product3.first << " is $" << product3.second << "\n";
  return 0;
}


Output:

The price of tomatoes is $3.25
The price of lightbulbs is $0.99
The price of shoes is $20

See also

make_pair
Construct pair object (function template )