Qt Toolkit - QMapIterator Class

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# QMapIterator Class Reference

The QMapIterator class provides an iterator for QMap. More...

`#include <qmap.h>`

List of all member functions.

## Public Members

- QMapIterator ()
- QMapIterator ( QMapNode<K, T> * p )
- QMapIterator ( const QMapIterator<K,T> & it )
- bool operator== ( const QMapIterator<K,T> & it ) const
- bool operator!= ( const QMapIterator<K,T> & it ) const
- T& operator* ()
- const T& operator* () const
- const K& key () const
- T& data ()
- const T& data () const

## Detailed Description

The QMapIterator class provides an iterator for QMap.

You can not create an iterator by yourself. Instead you have to ask a map to give you one. An iterator has only the size of a pointer. On 32 bit machines that means 4 bytes otherwise 8 bytes. That makes them very fast. In fact they resemble the semantics of pointers as good as possible and they are almost as fast as usual pointers.

Example:

        #include <qmap.h>
        #include <qstring.h>
        #include <stdio.h>

        class Employee
        {
        public:
            Employee(): s(0) {}
            Employee( const QString& name, int salary )
                : n(name), s(salary)
            {}

            QString     name()   const              { return n; }
            int         salary() const              { return s; }
            void        setSalary( int salary )     { s = salary; }
        private:
            QString     n;
            int         s;
        };

        void main()
        {
            typedef QMap<QString,Employee> EmployeeMap;
            EmployeeMap map;                // map of Employee

            map.insert( "Gates", Employee("Bill", 50000) );
            map.insert( "Ballmer", Employee("Steve",80000) );
            map.insert( "Sommer,", Employee("Ron",  60000) );

            Employee joe( "Joe", 50000 );
            map.insert( "Doe", joe );
            joe.setSalary( 4000 );

            EmployeeMap::Iterator it;
            for( it = map.begin(); it != map.end(); ++it )
                printf( "%s, %s earns %d\n", it.key().latin1(), it.data().name().latin1(), it.data().salary() );
        }

Program output:

            Ballmer, Steve earns 80000
            Doe, Joe earns 50000
            Gates, Bill earns 50000
            Sommer, Ron earns 60000

The only way to traverse a map is to use iterators. QMap is highly optimized for performance and memory usage. On the other hand that means that you have to be a bit more careful by what you are doing. QMap does not know about all its iterators and the iterators don't even know to which map they belong. That makes things fast and slim but a bit dangerous because it is up to you to make sure that iterators you are using are still valid. QDictIterator will be able to give warnings while QMapIterator may end up in an undefined state.

For every Iterator there is a ConstIterator. When accessing a QMap in a const environment or if the reference or pointer to the map is itself const, then you have to use the ConstIterator. Its semantics are the same, but it returns only const references to the item it points to.

See also QMap.

## Member Function Documentation

### QMapIterator::QMapIterator ()

Creates an uninitialized iterator.

### QMapIterator::QMapIterator ( QMapNode<K, T> * p )

Constructs an iterator starting at node p.

### QMapIterator::QMapIterator ( const QMapIterator<K,T> & it )

Constructs a copy of the iterator.

### T& QMapIterator::data ()

Returns a reference to the current item.

### const T& QMapIterator::data () const

Returns a const reference to the data of the current item.

### const K& QMapIterator::key () const

Returns a const reference to the data of the current key.

### bool QMapIterator::operator!= ( const QMapIterator<K,T> & it ) const

Compares both iterators and returns TRUE if they point to different items.

### T& QMapIterator::operator* ()

Asterix operator. Returns a reference to the current item. The same as data().

### const T& QMapIterator::operator* () const

Asterix operator. Returns a const reference to the current item. The same as data().

### bool QMapIterator::operator== ( const QMapIterator<K,T> & it ) const

Compares both iterators and returns TRUE if they point to the same item.

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