QPair Class

The QPair class is a template class that stores a pair of items. More...

Header: #include <QPair>
qmake: QT += core

Public Types

typedef first_type
typedef second_type

Public Variables

T1 first
T2 second
QPair<T1, T2> qMakePair(const T1 &x, const T2 &y)
bool operator!=(const int &p1, const int &p2)
bool operator==(const int &p1, const int &p2)

Detailed Description

QPair<T1, T2> can be used in your application if the STL pair type is not available. It stores one value of type T1 and one value of type T2. It can be used as a return value for a function that needs to return two values, or as the value type of a generic container.

Here's an example of a QPair that stores one QString and one double value:


  QPair<QString, double> pair;

The components are accessible as public data members called first and second. For example:


  pair.first = "pi";
  pair.second = M_PI;

Note, however, that it is almost always preferable to define a small struct to hold the result of a function with multiple return values. A struct trivially generalizes to more than two values, and allows more descriptive member names than first and second:


  struct Variable {
      QString name;
      double value;
  };
  Variable v;
  v.name = "pi";
  v.value = M_PI;

The advent of C++11 automatic variable type deduction (auto) shifts the emphasis from the type name to the name of functions and members. Thus, QPair, like std::pair and std::tuple, is mostly useful in generic (template) code, where defining a dedicated type is not possible.

QPair's template data types (T1 and T2) must be assignable data types. You cannot, for example, store a QWidget as a value; instead, store a QWidget *. A few functions have additional requirements; these requirements are documented on a per-function basis.

See also Container Classes.

Member Type Documentation

typedef QPair::first_type

The type of the first element in the pair (T1).

See also first.

typedef QPair::second_type

The type of the second element in the pair (T2).

See also second.

Member Variable Documentation

T1 QPair::first

The first element in the pair.

T2 QPair::second

The second element in the pair.

Related Non-Members

QPair<T1, T2> QPair::qMakePair(const T1 &x, const T2 &y)

Returns a QPair<T1, T2> that contains value1 and value2. Example:


  QList<QPair<int, double> > list;
  list.append(qMakePair(66, M_PI));

This is equivalent to QPair<T1, T2>(value1, value2), but usually requires less typing.

bool QPair::operator!=(const int &p1, const int &p2)

Returns true if lhs and rhs are different; otherwise returns false.

This function was introduced in Qt 5.0.

bool QPair::operator==(const int &p1, const int &p2)

Returns true if lhs and rhs are equal; otherwise returns false.

This function was introduced in Qt 5.0.