# QPair Class

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

Header: | #include <QPair> |

## Public Types

typedef | first_type |

typedef | second_type |

## Public Functions

QPair() | |

QPair(const T1 & value1, const T2 & value2) | |

QPair<T1, T2> & | operator=(const QPair<T1, T2> & other) |

## Public Variables

## Related Non-Members

QPair<T1, T2> | qMakePair(const T1 & value1, const T2 & value2) |

bool | operator!=(const QPair<T1, T2> & p1, const QPair<T1, T2> & p2) |

bool | operator<(const QPair<T1, T2> & p1, const QPair<T1, T2> & p2) |

QDataStream & | operator<<(QDataStream & out, const QPair<T1, T2> & pair) |

bool | operator<=(const QPair<T1, T2> & p1, const QPair<T1, T2> & p2) |

bool | operator==(const QPair<T1, T2> & p1, const QPair<T1, T2> & p2) |

bool | operator>(const QPair<T1, T2> & p1, const QPair<T1, T2> & p2) |

bool | operator>=(const QPair<T1, T2> & p1, const QPair<T1, T2> & p2) |

QDataStream & | operator>>(QDataStream & in, QPair<T1, T2> & pair) |

## Detailed Description

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

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 = 3.14159265358979323846;

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 Function Documentation

### QPair::QPair()

Constructs an empty pair. The `first`

and `second`

elements are initialized with default-constructed values.

### QPair::QPair(const T1 &* value1*, const T2 &* value2*)

Constructs a pair and initializes the `first`

element with *value1* and the `second`

element with *value2*.

**See also **qMakePair().

### QPair<T1, T2> & QPair::operator=(const QPair<T1, T2> &* other*)

Assigns *other* to this pair.

## 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> qMakePair(const T1 &* value1*, const T2 &* value2*)

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

QList<QPair<int, double> > list; list.append(qMakePair(66, 3.14159));

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

### bool operator!=(const QPair<T1, T2> &* p1*, const QPair<T1, T2> &* p2*)

Returns true if *p1* is not equal to *p2*; otherwise returns false. Two pairs compare as not equal if their `first`

data members are not equal or if their `second`

data members are not equal.

This function requires the T1 and T2 types to have an implementation of `operator==()`

.

### bool operator<(const QPair<T1, T2> &* p1*, const QPair<T1, T2> &* p2*)

Returns true if *p1* is less than *p2*; otherwise returns false. The comparison is done on the `first`

members of *p1* and *p2*; if they compare equal, the `second`

members are compared to break the tie.

This function requires the T1 and T2 types to have an implementation of `operator<()`

.

### QDataStream & operator<<(QDataStream &* out*, const QPair<T1, T2> &* pair*)

Writes the pair *pair* to stream *out*.

This function requires the T1 and T2 types to implement `operator<<()`

.

**See also **Serializing Qt Data Types.

### bool operator<=(const QPair<T1, T2> &* p1*, const QPair<T1, T2> &* p2*)

Returns true if *p1* is less than or equal to *p2*; otherwise returns false. The comparison is done on the `first`

members of *p1* and *p2*; if they compare equal, the `second`

members are compared to break the tie.

This function requires the T1 and T2 types to have an implementation of `operator<()`

.

### bool operator==(const QPair<T1, T2> &* p1*, const QPair<T1, T2> &* p2*)

Returns true if *p1* is equal to *p2*; otherwise returns false. Two pairs compare equal if their `first`

data members compare equal and if their `second`

data members compare equal.

This function requires the T1 and T2 types to have an implementation of `operator==()`

.

### bool operator>(const QPair<T1, T2> &* p1*, const QPair<T1, T2> &* p2*)

Returns true if *p1* is greater than *p2*; otherwise returns false. The comparison is done on the `first`

members of *p1* and *p2*; if they compare equal, the `second`

members are compared to break the tie.

This function requires the T1 and T2 types to have an implementation of `operator<()`

.

### bool operator>=(const QPair<T1, T2> &* p1*, const QPair<T1, T2> &* p2*)

Returns true if *p1* is greater than or equal to *p2*; otherwise returns false. The comparison is done on the `first`

members of *p1* and *p2*; if they compare equal, the `second`

members are compared to break the tie.

This function requires the T1 and T2 types to have an implementation of `operator<()`

.

### QDataStream & operator>>(QDataStream &* in*, QPair<T1, T2> &* pair*)

Reads a pair from stream *in* into *pair*.

This function requires the T1 and T2 types to implement `operator>>()`

.

**See also **Serializing Qt Data Types.

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