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QMultiHash Class ReferenceThe QMultiHash class is a convenience QHash subclass that provides multi-valued hashes. More... #include <QMultiHash>Inherits: QHash<Key, T>. Note: All functions in this class are reentrant. Public Functions
Detailed DescriptionThe QMultiHash class is a convenience QHash subclass that provides multi-valued hashes. QMultiHash<Key, T> is one of Qt's generic container classes. It inherits QHash and extends it with a few convenience functions that make it more suitable than QHash for storing multi-valued hashes. A multi-valued hash is a hash that allows multiple values with the same key; QHash normally doesn't allow that, unless you call QHash::insertMulti(). Because QMultiHash inherits QHash, all of QHash's functionality also applies to QMultiHash. For example, you can use isEmpty() to test whether the hash is empty, and you can traverse a QMultiHash using QHash's iterator classes (for example, QHashIterator). But in addition, it provides an insert() function that corresponds to QHash::insertMulti(), and a replace() function that corresponds to QHash::insert(). It also provides convenient operator+() and operator+=(). Example: QMultiHash<QString, int> hash1, hash2, hash3; hash1.insert("plenty", 100); hash1.insert("plenty", 2000); // hash1.size() == 2 hash2.insert("plenty", 5000); // hash2.size() == 1 hash3 = hash1 + hash2; // hash3.size() == 3 Unlike QHash, QMultiHash provides no operator[]. Use value() or replace() if you want to access the most recently inserted item with a certain key. If you want to retrieve all the values for a single key, you can use values(const Key &key), which returns a QList<T>: QList<int> values = hash.values("plenty"); for (int i = 0; i < values.size(); ++i) cout << values.at(i) << endl; The items that share the same key are available from most recently to least recently inserted. A more efficient approach is to call find() to get the STL-style iterator for the first item with a key and iterate from there: QMultiHash<QString, int>::iterator i = hash.find("plenty"); while (i != hash.end() && i.key() == "plenty") { cout << i.value() << endl; ++i; } QMultiHash's key and value data types must be assignable data types. You cannot, for example, store a QWidget as a value; instead, store a QWidget *. In addition, QMultiHash's key type must provide operator==(), and there must also be a global qHash() function that returns a hash value for an argument of the key's type. See the QHash documentation for details. See also QHash, QHashIterator, QMutableHashIterator, and QMultiMap. Member Function Documentation
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