Qt 4.0: QPair Class Reference

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# QPair Class Reference
[QtCore module]

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

    #include <QPair>

- List of all members, including inherited members

### Public Types

- typedef first_type
- typedef second_type

### Public Functions

- QPair ()
- QPair ( const T1 & value1, const T2 & value2 )
- QPair & operator= ( const QPair & other )

### Public Variables

- T1 first
- T2 second

### 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 Generic Containers.

## 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 & QPair::operator= ( const QPair & 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 )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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 )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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 )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Writes the pair pair to stream out.

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

See also Format of the QDataStream operators.

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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 )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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 )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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 )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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 )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Reads a pair from stream in into pair.

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

See also Format of the QDataStream operators.