src_corelib_tools_qhash.cpp

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// Copyright (C) 2020 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
 
#include <QHash>
#include <QHashIterator>
#include <iostream>
#include <QDate>
 
#include <utility>
 
using namespace std;
 
void examples()
{
    //! [0]
    QHash<QString, int> hash;
    //! [0]
 
    {
        //! [1]
        hash["one"] = 1;
        hash["three"] = 3;
        hash["seven"] = 7;
        //! [1]
    }
 
    {
        //! [2]
        hash.insert("twelve", 12);
        //! [2]
    }
 
    {
        //! [3]
        int num1 = hash["thirteen"];
        int num2 = hash.value("thirteen");
        //! [3]
    }
 
    {
        //! [4]
        int timeout = 30;
        if (hash.contains("TIMEOUT"))
            timeout = hash.value("TIMEOUT");
        //! [4]
    }
 
    {
        //! [5]
        int timeout = hash.value("TIMEOUT", 30);
        //! [5]
    }
 
    {
        //! [7]
        QHashIterator<QString, int> i(hash);
        while (i.hasNext()) {
            i.next();
            cout << qPrintable(i.key()) << ": " << i.value() << endl;
        }
        //! [7]
    }
 
    {
        //! [8]
        for (const auto &[key, value] : std::as_const(hash).asKeyValueRange())
            cout << qPrintable(key) << ": " << value << endl;
        //! [8]
    }
 
    {
        //! [qhash-iterator-stl-style]
        for (auto it = hash.cbegin(); it != hash.cend(); ++it)
            cout << qPrintable(it.key()) << ": " << it.value() << endl;
        //! [qhash-iterator-stl-style]
    }
 
    {
        //! [qhash-iterator-modify-values]
        for (auto it = hash.begin(); it != hash.end(); ++it)
            it.value() += 1;
        //! [qhash-iterator-modify-values]
    }
 
    {
        //! [9]
        hash.insert("plenty", 100);
        hash.insert("plenty", 2000);
        // hash.value("plenty") == 2000
        //! [9]
    }
 
    {
        //! [12]
        QHash<QString, int> hash;
        //...
        for (int value : std::as_const(hash))
            cout << value << endl;
        //! [12]
    }
}
 
#if __has_include(<QWidget>)
#include <QWidget>
 
void widget_example(QWidget *okButton)
{
    //! [6]
    // WRONG
    QHash<int, QWidget *> hash;
    //...
    for (int i = 0; i < 1000; ++i) {
        if (hash[i] == okButton)
            cout << "Found button at index " << i << endl;
    }
    //! [6]
}
#endif
 
//! [13]
#ifndef EMPLOYEE_H
#define EMPLOYEE_H
 
class Employee
{
public:
    Employee() {}
    Employee(const QString &name, QDate dateOfBirth);
    QString name() const { return myName; }
    QDate dateOfBirth() const { return myDateOfBirth; }
    //...
 
private:
    QString myName;
    QDate myDateOfBirth;
};
 
inline bool operator==(const Employee &e1, const Employee &e2)
{
    return e1.name() == e2.name()
           && e1.dateOfBirth() == e2.dateOfBirth();
}
 
inline size_t qHash(const Employee &key, size_t seed)
{
    return qHashMulti(seed, key.name(), key.dateOfBirth());
}
 
#endif // EMPLOYEE_H
//! [13]
 
 
void wrap()
{
    {
        QString keys[1];
        int values[1];
 
        //! [14]
        QHash<QString, int> hash;
        hash.reserve(20000);
        for (int i = 0; i < 20000; ++i)
            hash.insert(keys[i], values[i]);
        //! [14]
    }
 
    {
        QObject *obj;
 
        //! [15]
        QHash<QObject *, int> objectHash;
        //...
        QHash<QObject *, int>::iterator i = objectHash.find(obj);
        while (i != objectHash.end() && i.key() == obj) {
            if (i.value() == 0) {
                i = objectHash.erase(i);
            } else {
                ++i;
            }
        }
        //! [15]
    }
 
    {
        QObject *obj;
 
        //! [15multihash]
        QMultiHash<QObject *, int> objectHash;
        //...
        QMultiHash<QObject *, int>::iterator i = objectHash.find(obj);
        while (i != objectHash.end() && i.key() == obj) {
            if (i.value() == 0) {
                i = objectHash.erase(i);
            } else {
                ++i;
            }
        }
        //! [15multihash]
    }
 
    {
        //! [16]
        QHash<QString, int> hash;
        //...
        QHash<QString, int>::const_iterator i = hash.find("HDR");
        while (i != hash.end() && i.key() == "HDR") {
            cout << i.value() << endl;
            ++i;
        }
        //! [16]
    }
 
    {
        //! [17]
        QHash<QString, int> hash;
        hash.insert("January", 1);
        hash.insert("February", 2);
        //...
        hash.insert("December", 12);
 
        for (auto i = hash.cbegin(), end = hash.cend(); i != end; ++i)
            cout << qPrintable(i.key()) << ": " << i.value() << endl;
        //! [17]
    }
 
    {
        QHash<QString, int> hash;
 
        //! [18]
        for (auto i = hash.begin(), end = hash.end(); i != end; ++i)
            i.value() += 2;
        //! [18]
    }
 
    {
        QHash<QString, int> hash;
 
        //! [21]
        erase_if(hash, [](const QHash<QString, int>::iterator it) { return it.value() > 10; });
        //! [21]
    }
 
    {
        QHash<QString, QString> hash;
        auto i = hash.begin();
 
        //! [22]
        if (i.key() == "Hello")
            i.value() = "Bonjour";
        //! [22]
    }
 
    {
    //! [23]
        QHash<QString, int> hash;
        hash.insert("January", 1);
        hash.insert("February", 2);
        //...
        hash.insert("December", 12);
 
        for (auto i = hash.cbegin(), end = hash.cend(); i != end; ++i)
            cout << qPrintable(i.key()) << ": " << i.value() << endl;
        //! [23]
    }
 
    {
        //! [24]
        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
        //! [24]
    }
 
    {
        QMultiHash<QString, int> hash;
 
        //! [25]
        QList<int> values = hash.values("plenty");
        for (auto i : std::as_const(values))
            cout << i << endl;
        //! [25]
    }
 
    {
        QMultiHash<QString, int> hash;
 
        //! [26]
        auto i = hash.constFind("plenty");
        while (i != hash.cend() && i.key() == "plenty") {
            cout << i.value() << endl;
            ++i;
        }
        //! [26]
    }
 
    {
        QMultiHash<int, QString> hash;
 
        //! [27]
        for (auto it = hash.cbegin(), end = hash.cend(); it != end; ++it) {
            cout << "The key: " << it.key() << endl;
            cout << "The value: " << qPrintable(it.value()) << endl;
            cout << "Also the value: " << qPrintable(*it) << endl;
        }
        //! [27]
    }
 
    {
        QHash<int, int> hash;
        QHash<QObject *, int> hash2;
        auto isPrimeNumber = [](int num) { return true; };
 
        //! [28]
        // Inefficient, keys() is expensive
        QList<int> keys = hash.keys();
        int numPrimes = std::count_if(keys.cbegin(), keys.cend(), isPrimeNumber);
        qDeleteAll(hash2.keys());
 
        // Efficient, no memory allocation needed
        int primeNums = std::count_if(hash.keyBegin(), hash.keyEnd(), isPrimeNumber);
        qDeleteAll(hash2.keyBegin(), hash2.keyEnd());
        //! [28]
    }
}
 
//! [qhashbits]
inline size_t qHash(const std::vector<int> &key, size_t seed = 0)
{
    if (key.empty())
        return seed;
    else
        return qHashBits(&key.front(), key.size() * sizeof(int), seed);
}
//! [qhashbits]
 
namespace Repetition_1
{
    //! [qhashrange]
    inline size_t qHash(const std::vector<int> &key, size_t seed = 0)
    {
        return qHashRange(key.begin(), key.end(), seed);
    }
    //! [qhashrange]
}
 
namespace Repetition_2
{
    //! [qhashrangecommutative]
    inline size_t qHash(const std::unordered_set<int> &key, size_t seed = 0)
    {
        return qHashRangeCommutative(key.begin(), key.end(), seed);
    }
    //! [qhashrangecommutative]
}
 
#if TEXT
//! [30]
{0, 1, 2}
//! [30]
 
//! [31]
{1, 2, 0}
//! [31]
#endif
 
struct K {};
 
void snippets()
{
    {
        //! [32]
        size_t qHash(K key, size_t seed);
        size_t qHash(const K &key, size_t seed);
 
        size_t qHash(K key);        // deprecated, do not use
        size_t qHash(const K &key); // deprecated, do not use
        //! [32]
    }
 
    {
        //! [34]
        QHash<QString, int> hash;
        hash.insert("January", 1);
        hash.insert("February", 2);
        // ...
        hash.insert("December", 12);
 
        for (auto [key, value] : hash.asKeyValueRange()) {
            cout << qPrintable(key) << ": " << value << endl;
            --value; // convert to JS month indexing
        }
        //! [34]
    }
 
    {
        //! [35]
        QMultiHash<QString, int> hash;
        hash.insert("January", 1);
        hash.insert("February", 2);
        // ...
        hash.insert("December", 12);
 
        for (auto [key, value] : hash.asKeyValueRange()) {
            cout << qPrintable(key) << ": " << value << endl;
            --value; // convert to JS month indexing
        }
        //! [35]
    }
}
 
//! [33]
namespace std
{
    template <> struct hash<K>
    {
        // seed is optional
        size_t operator()(const K &key, size_t seed = 0) const;
    };
}
//! [33]