QMap Class Reference

 #include <QMap>

 QMap<QString, int> map;

 map["one"] = 1;
 map["three"] = 3;
 map["seven"] = 7;

 map.insert("twelve", 12);

 int num1 = map["thirteen"];
 int num2 = map.value("thirteen");

 int timeout = 30;
 if (map.contains("TIMEOUT"))
     timeout = map.value("TIMEOUT");

 int timeout = map.value("TIMEOUT", 30);

 // WRONG
 QMap<int, QWidget *> map;
 ...
 for (int i = 0; i < 1000; ++i) {
     if (map[i] == okButton)
         cout << "Found button at index " << i << endl;
 }

 QMapIterator<QString, int> i(map);
 while (i.hasNext()) {
     i.next();
     cout << i.key() << ": " << i.value() << endl;
 }

 QMap<QString, int>::const_iterator i = map.constBegin();
 while (i != map.constEnd()) {
     cout << i.key() << ": " << i.value() << endl;
     ++i;
 }

 map.insert("plenty", 100);
 map.insert("plenty", 2000);
 // map.value("plenty") == 2000

 QList<int> values = map.values("plenty");
 for (int i = 0; i < values.size(); ++i)
     cout << values.at(i) << endl;

 QMap<QString, int>::iterator i = map.find("plenty");
 while (i != map.end() && i.key() == "plenty") {
     cout << i.value() << endl;
     ++i;
 }

 QMap<QString, int> map;
 ...
 foreach (int value, map)
     cout << value << endl;

 #ifndef EMPLOYEE_H
 #define EMPLOYEE_H

 class Employee
 {
 public:
     Employee() {}
     Employee(const QString &name, const QDate &dateOfBirth);
     ...

 private:
     QString myName;
     QDate myDateOfBirth;
 };

 inline bool operator<(const Employee &e1, const Employee &e2)
 {
     if (e1.name() != e2.name())
         return e1.name() < e2.name();
     return e1.dateOfBirth() < e2.dateOfBirth();
 }

 #endif // EMPLOYEE_H

Member Function Documentation

QMap::QMap ()

Constructs an empty map.

See also clear().

QMap::QMap ( const QMap<Key, T> & other )

Constructs a copy of other.

This operation occurs in constant time, because QMap is implicitly shared. This makes returning a QMap from a function very fast. If a shared instance is modified, it will be copied (copy-on-write), and this takes linear time.

See also operator=().

QMap::QMap ( const std::map<Key, T> & other )

Constructs a copy of other.

This function is only available if Qt is configured with STL compatibility enabled.

See also toStdMap().

QMap::~QMap ()

Destroys the map. References to the values in the map, and all iterators over this map, become invalid.

iterator QMap::begin ()

Returns an STL-style iterator pointing to the first item in the map.

See also constBegin() and end().

const_iterator QMap::begin () const

This is an overloaded function.

void QMap::clear ()

Removes all items from the map.

See also remove().

const_iterator QMap::constBegin () const

Returns a const STL-style iterator pointing to the first item in the map.

See also begin() and constEnd().

const_iterator QMap::constEnd () const

Returns a const STL-style iterator pointing to the imaginary item after the last item in the map.

See also constBegin() and end().

const_iterator QMap::constFind ( const Key & key ) const

Returns an const iterator pointing to the item with key key in the map.

If the map contains no item with key key, the function returns constEnd().

This function was introduced in Qt 4.1.

See also find() and QMultiMap::constFind().

bool QMap::contains ( const Key & key ) const

Returns true if the map contains an item with key key; otherwise returns false.

See also count() and QMultiMap::contains().

int QMap::count ( const Key & key ) const

Returns the number of items associated with key key.

See also contains(), insertMulti(), and QMultiMap::count().

int QMap::count () const

This is an overloaded function.

Same as size().

bool QMap::empty () const

This function is provided for STL compatibility. It is equivalent to isEmpty(), returning true if the map is empty; otherwise returning false.

iterator QMap::end ()

Returns an STL-style iterator pointing to the imaginary item after the last item in the map.

See also begin() and constEnd().

const_iterator QMap::end () const

This is an overloaded function.

iterator QMap::erase ( iterator pos )

Removes the (key, value) pair pointed to by the iterator pos from the map, and returns an iterator to the next item in the map.

See also remove().

iterator QMap::find ( const Key & key )

Returns an iterator pointing to the item with key key in the map.

If the map contains no item with key key, the function returns end().

If the map contains multiple items with key key, this function returns an iterator that points to the most recently inserted value. The other values are accessible by incrementing the iterator. For example, here's some code that iterates over all the items with the same key:

 QMap<QString, int> map;
 ...
 QMap<QString, int>::const_iterator i = map.find("HDR");
 while (i != map.end() && i.key() == "HDR") {
     cout << i.value() << endl;
     ++i;
 }

See also constFind(), value(), values(), lowerBound(), upperBound(), and QMultiMap::find().

const_iterator QMap::find ( const Key & key ) const

This is an overloaded function.

iterator QMap::insert ( const Key & key, const T & value )

Inserts a new item with the key key and a value of value.

If there is already an item with the key key, that item's value is replaced with value.

If there are multiple items with the key key, the most recently inserted item's value is replaced with value.

See also insertMulti().

iterator QMap::insertMulti ( const Key & key, const T & value )

Inserts a new item with the key key and a value of value.

If there is already an item with the same key in the map, this function will simply create a new one. (This behavior is different from insert(), which overwrites the value of an existing item.)

See also insert() and values().

bool QMap::isEmpty () const

Returns true if the map contains no items; otherwise returns false.

See also size().

const Key QMap::key ( const T & value ) const

Returns the first key with value value.

If the map contains no item with value value, the function returns a default-constructed key.

This function can be slow (linear time), because QMap's internal data structure is optimized for fast lookup by key, not by value.

See also value() and keys().

const Key QMap::key ( const T & value, const Key & defaultKey ) const

This is an overloaded function.

Returns the first key with value value, or defaultKey if the map contains no item with value value.

This function can be slow (linear time), because QMap's internal data structure is optimized for fast lookup by key, not by value.

This function was introduced in Qt 4.3.

QList<Key> QMap::keys () const

Returns a list containing all the keys in the map in ascending order. Keys that occur multiple times in the map (because items were inserted with insertMulti(), or unite() was used) also occur multiple times in the list.

To obtain a list of unique keys, where each key from the map only occurs once, use uniqueKeys().

The order is guaranteed to be the same as that used by values().

See also uniqueKeys(), values(), and key().

QList<Key> QMap::keys ( const T & value ) const

This is an overloaded function.

Returns a list containing all the keys associated with value value in ascending order.

This function can be slow (linear time), because QMap's internal data structure is optimized for fast lookup by key, not by value.

iterator QMap::lowerBound ( const Key & key )

Returns an iterator pointing to the first item with key key in the map. If the map contains no item with key key, the function returns an iterator to the nearest item with a greater key.

Example:

 QMap<int, QString> map;
 map.insert(1, "one");
 map.insert(5, "five");
 map.insert(10, "ten");

 map.lowerBound(0);      // returns iterator to (1, "one")
 map.lowerBound(1);      // returns iterator to (1, "one")
 map.lowerBound(2);      // returns iterator to (5, "five")
 map.lowerBound(10);     // returns iterator to (10, "ten")
 map.lowerBound(999);    // returns end()

If the map contains multiple items with key key, this function returns an iterator that points to the most recently inserted value. The other values are accessible by incrementing the iterator. For example, here's some code that iterates over all the items with the same key:

 QMap<QString, int> map;
 ...
 QMap<QString, int>::const_iterator i = map.lowerBound("HDR");
 QMap<QString, int>::const_iterator upperBound = map.upperBound("HDR");
 while (i != upperBound) {
     cout << i.value() << endl;
     ++i;
 }

See also qLowerBound(), upperBound(), and find().

const_iterator QMap::lowerBound ( const Key & key ) const

This is an overloaded function.

int QMap::remove ( const Key & key )

Removes all the items that have the key key from the map. Returns the number of items removed which is usually 1 but will be 0 if the key isn't in the map, or > 1 if insertMulti() has been used with the key.

See also clear(), take(), and QMultiMap::remove().

int QMap::size () const

Returns the number of (key, value) pairs in the map.

See also isEmpty() and count().

T QMap::take ( const Key & key )

Removes the item with the key key from the map and returns the value associated with it.

If the item does not exist in the map, the function simply returns a default-constructed value. If there are multiple items for key in the map, only the most recently inserted one is removed and returned.

If you don't use the return value, remove() is more efficient.

See also remove().

std::map<Key, T> QMap::toStdMap () const

Returns an STL map equivalent to this QMap.

This function is only available if Qt is configured with STL compatibility enabled.

QList<Key> QMap::uniqueKeys () const

Returns a list containing all the keys in the map in ascending order. Keys that occur multiple times in the map (because items were inserted with insertMulti(), or unite() was used) occur only once in the returned list.

This function was introduced in Qt 4.2.

See also keys() and values().

QMap<Key, T> & QMap::unite ( const QMap<Key, T> & other )

Inserts all the items in the other map into this map. If a key is common to both maps, the resulting map will contain the key multiple times.

See also insertMulti().

iterator QMap::upperBound ( const Key & key )

Returns an iterator pointing to the item that immediately follows the last item with key key in the map. If the map contains no item with key key, the function returns an iterator to the nearest item with a greater key.

Example:

 QMap<int, QString> map;
 map.insert(1, "one");
 map.insert(5, "five");
 map.insert(10, "ten");

 map.upperBound(0);      // returns iterator to (1, "one")
 map.upperBound(1);      // returns iterator to (5, "five")
 map.upperBound(2);      // returns iterator to (5, "five")
 map.upperBound(10);     // returns end()
 map.upperBound(999);    // returns end()

See also qUpperBound(), lowerBound(), and find().

const_iterator QMap::upperBound ( const Key & key ) const

This is an overloaded function.

const T QMap::value ( const Key & key ) const

Returns the value associated with the key key.

If the map contains no item with key key, the function returns a default-constructed value. If there are multiple items for key in the map, the value of the most recently inserted one is returned.

See also key(), values(), contains(), and operator[]().

const T QMap::value ( const Key & key, const T & defaultValue ) const

This is an overloaded function.

If the map contains no item with key key, the function returns defaultValue.

QList<T> QMap::values () const

Returns a list containing all the values in the map, in ascending order of their keys. If a key is associated with multiple values, all of its values will be in the list, and not just the most recently inserted one.

See also keys() and value().

QList<T> QMap::values ( const Key & key ) const

This is an overloaded function.

Returns a list containing all the values associated with key key, from the most recently inserted to the least recently inserted one.

See also count() and insertMulti().

bool QMap::operator!= ( const QMap<Key, T> & other ) const

Returns true if other is not equal to this map; otherwise returns false.

Two maps are considered equal if they contain the same (key, value) pairs.

This function requires the value type to implement operator==().

See also operator==().

QMap<Key, T> & QMap::operator= ( const QMap<Key, T> & other )

Assigns other to this map and returns a reference to this map.

bool QMap::operator== ( const QMap<Key, T> & other ) const

Returns true if other is equal to this map; otherwise returns false.

Two maps are considered equal if they contain the same (key, value) pairs.

This function requires the value type to implement operator==().

See also operator!=().

T & QMap::operator[] ( const Key & key )

Returns the value associated with the key key as a modifiable reference.

If the map contains no item with key key, the function inserts a default-constructed value into the map with key key, and returns a reference to it. If the map contains multiple items with key key, this function returns a reference to the most recently inserted value.

See also insert() and value().

const T QMap::operator[] ( const Key & key ) const

This is an overloaded function.

Same as value().