QT STL type iterator

1. brief introduction

STL Iterator and Qt and STL Compatible with native algorithms , And the speed is optimized ; For every container class , There are two STL Type iterators ： One for read-only access , One for read-write access . It is recommended to use a read-only iterator when there is no need to modify the data , Because it's faster .

The following table is a summary of types ：

STL Iterator class of type

Container class	Read only iterator	Read write iterator
QList<T>, QQueue<T>	QList<T>::const iterator	QList<T>::iterator
QLinkedList<T>	Q1. i nked List<1>: :const_iterator	QLinkedList<T>::iterator
QVector<T>, QStack<T>	QVector<T>::const_ilerator	QVector<T>::iterator
QSet<T>	QSet<T>::const_iterator	QSet<T>::iterator
QMap<Key, P> QMultiMap<Kcy, T>	QMap<Key, T>::const_iterator	QMap<Key, T>:: iterator
QHash<Key, T> QMultiHash<Key, T>	QHash<Key, T>: :const_iterator	QHash<Key, T>::iterator

The difference between defining read-only iterators and read-write iterators , They use different key words ,const_iterator Define a read-only iterator ,iterator Define read-write iterators .

Besides , You can also use const_reverse_iterator and reverse_iterator Define the corresponding inverse iterator .

STL An iterator of type is a pointer to an array , therefore “++” Operator causes the iterator to point to the next data item , Operator returns the contents of the data item .STL Iterators point directly to data items .

• begin() Point to the first data item of the container
• end() Is an invalid data item , End of the said

2. Example

Use QList Read only iterators traverse the output data .

QList<QString> list;
list << "1" << "2" << "3" << "4";
QList<QString>::const_iterator i;
for (i = list.constBegin(); i != list.constEnd(); ++i)
    qDebug() << *i;

Use QMap Read only iterators traverse the output data .

QMap<int, int> map;
map[1] = 1;
map[2] = 2;
map[3] = 3;

QMap<int, int>::const_iterator i;
for (i = map.constBegin(); i != map.constEnd(); ++i)
    qDebug () << i.key () << ':' << i.value ();