QSet使用及Qt自定义类型使用QHash等算法

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本文标题:QSet使用及Qt自定义类型使用QHash等算法     本文地址:http://techieliang.com/2017/12/580/

1. 介绍

Qt提供的一个单值的数学集合的快速查找容器,使用方式与QList相同,但其内元素不会有重复。详细说明见 官方文档

注意,此容器实现方式是基于哈希表,而不是红黑树,若使用自定义类必须提供对应的hash函数:

QSet‘s value data type must be an assignable data type. You cannot, for example, store a QWidget as a value; instead, store a QWidget *. In addition, the 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 a list of types supported by qHash().

2. 简单范例

  1. QSet <QString> m_set;
  2. m_set.insert("1");
  3. m_set.insert("3");
  4. m_set.insert("2");//注意插入顺序
  5. auto b_set = m_set.begin();
  6. qDebug()<<m_set.size();
  7. qDebug()<<*b_set++;
  8. qDebug()<<*b_set++;
  9. qDebug()<<*b_set++;//注意存储顺序
  10. m_set.insert("1");//插入重复的
  11. b_set = m_set.begin();
  12. qDebug()<<m_set.size();
  13. qDebug()<<*b_set++;
  14. qDebug()<<*b_set++;
  15. qDebug()<<*b_set++;

结果

  1. 3
  2. "1"
  3. "2"
  4. "3"
  5. 3
  6. "1"
  7. "2"
  8. "3"

3. 自定义类型

  1. #include <QCoreApplication>
  2. #include <QSet>
  3. #include <QDebug>
  4. class testCustomTypeByQSet {
  5. public:
  6. testCustomTypeByQSet(int v):m_value(v){};
  7. int value() const{
  8. return m_value;
  9. }
  10. bool operator == (const testCustomTypeByQSet &t) const {
  11. return (m_value==t.value());
  12. }
  13. private:
  14. int m_value;
  15. };
  16. uint qHash(const testCustomTypeByQSet &key, uint seed = 0) {
  17. return key.value();
  18. }
  19. int main(int argc, char *argv[]) {
  20. QCoreApplication a(argc, argv);
  21. QSet<testCustomTypeByQSet> m_set;
  22. m_set.insert(testCustomTypeByQSet(1));
  23. m_set.insert(testCustomTypeByQSet(3));
  24. m_set.insert(testCustomTypeByQSet(2));
  25. m_set.insert(testCustomTypeByQSet(7));
  26. m_set.insert(testCustomTypeByQSet(-1));
  27. auto b_set = m_set.begin();
  28. qDebug()<<m_set.size();
  29. qDebug()<<(*b_set++).value();
  30. qDebug()<<(*b_set++).value();
  31. qDebug()<<(*b_set++).value();
  32. qDebug()<<(*b_set++).value();
  33. qDebug()<<(*b_set++).value();
  34. return 0;
  35. }

结果

  1. 5
  2. -1
  3. 1
  4. 2
  5. 3
  6. 7

qt自身的类已经实现了对应的qHash,存储在QHash类中,详见官方文档

  1. uint qHash(const QXmlNodeModelIndex &index)
  2. uint qHash(const QUrl &url, uint seed = 0)
  3. uint qHash(const QDateTime &key, uint seed = 0)
  4. uint qHash(const QDate &key, uint seed = 0)
  5. uint qHash(const QTime &key, uint seed = 0)
  6. uint qHash(const QPair<T1, T2> &key, uint seed = 0)
  7. uint qHash(const std::pair<T1, T2> &key, uint seed = 0)
  8. uint qHash(char key, uint seed = 0)
  9. uint qHash(uchar key, uint seed = 0)
  10. uint qHash(signed char key, uint seed = 0)
  11. uint qHash(ushort key, uint seed = 0)
  12. uint qHash(short key, uint seed = 0)
  13. uint qHash(uint key, uint seed = 0)
  14. uint qHash(int key, uint seed = 0)
  15. uint qHash(ulong key, uint seed = 0)
  16. uint qHash(long key, uint seed = 0)
  17. uint qHash(quint64 key, uint seed = 0)
  18. uint qHash(qint64 key, uint seed = 0)
  19. uint qHash(float key, uint seed = 0)
  20. uint qHash(double key, uint seed = 0)
  21. uint qHash(const QChar key, uint seed = 0)
  22. uint qHash(const QByteArray &key, uint seed = 0)
  23. uint qHash(const QBitArray &key, uint seed = 0)
  24. uint qHash(const QString &key, uint seed = 0)
  25. uint qHash(const QStringRef &key, uint seed = 0)
  26. uint qHash(QLatin1String key, uint seed = 0)
  27. uint qHash(const T *key, uint seed = 0)
  28. uint qHash(const QHash<Key, T> &key, uint seed = 0)
  29. uint qHash(const QSet<T> &key, uint seed = 0)
  30. uint qHash(const QVersionNumber &key, uint seed = 0)
  31. uint qHash(const QSslCertificate &key, uint seed = 0)
  32. uint qHash(QSslEllipticCurve curve, uint seed = 0)
  33. uint qHash(const QSslError &key, uint seed = 0)
  34. uint qHash(const QGeoCoordinate &coordinate, uint seed = 0)

同时也在对应类中做了“==”的重载操作符,比如QString类

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