src_corelib_tools_qmultimap.cpp

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// Copyright (C) 2020 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
 
QMultiMap<QString, int> multimap;
 
 
multimap.insert("a", 1);
multimap.insert("b", 3);
multimap.insert("c", 7);
multimap.insert("c", -5);
 
 
int num2 = multimap.value("a"); // 1
int num3 = multimap.value("thirteen"); // not found; 0
int num3 = 0;
auto it = multimap.constFind("b");
if (it != multimap.cend()) {
    num3 = it.value();
}
 
 
int timeout = 30;
if (multimap.contains("TIMEOUT"))
    timeout = multimap.value("TIMEOUT");
 
// better:
auto it = multimap.find("TIMEOUT");
if (it != multimap.end())
    timeout = it.value();
 
 
int timeout = multimap.value("TIMEOUT", 30);
 
 
QMultiMapIterator<QString, int> i(multimap);
while (i.hasNext()) {
    i.next();
    cout << qPrintable(i.key()) << ": " << i.value() << endl;
}
 
 
for (auto i = multimap.cbegin(), end = multimap.cend(); i != end; ++i)
    cout << qPrintable(i.key()) << ": " << i.value() << endl;
 
 
multimap.insert("plenty", 100);
multimap.insert("plenty", 2000);
// multimap.size() == 2
 
 
QList<int> values = multimap.values("plenty");
for (auto i : std::as_const(values))
    cout << i << endl;
 
 
auto i = multimap.find("plenty");
while (i != map.end() && i.key() == "plenty") {
    cout << i.value() << endl;
    ++i;
}
 
// better:
auto [i, end] = multimap.equal_range("plenty");
while (i != end) {
    cout << i.value() << endl;
    ++i;
}
 
 
QMap<QString, int> multimap;
...
for (int value : std::as_const(multimap))
    cout << value << endl;
 
 
#ifndef EMPLOYEE_H
#define EMPLOYEE_H
 
class Employee
{
public:
    Employee() {}
    Employee(const QString &name, QDate dateOfBirth);
    ...
 
private:
    QString myName;
    QDate myDateOfBirth;
};
 
inline bool operator<(const Employee &e1, const Employee &e2)
{
    if (e1.name() != e2.name())
        return e1.name() < e2.name();
    return e1.dateOfBirth() < e2.dateOfBirth();
}
 
#endif // EMPLOYEE_H
 
 
QMultiMap<int, QString> multimap;
multimap.insert(1, "one");
multimap.insert(5, "five");
multimap.insert(5, "five (2)");
multimap.insert(10, "ten");
 
multimap.lowerBound(0);      // returns iterator to (1, "one")
multimap.lowerBound(1);      // returns iterator to (1, "one")
multimap.lowerBound(2);      // returns iterator to (5, "five")
multimap.lowerBound(5);      // returns iterator to (5, "five")
multimap.lowerBound(6);      // returns iterator to (10, "ten")
multimap.lowerBound(10);     // returns iterator to (10, "ten")
multimap.lowerBound(999);    // returns end()
 
 
QMap<QString, int> multimap;
...
QMap<QString, int>::const_iterator i = multimap.lowerBound("HDR");
QMap<QString, int>::const_iterator upperBound = multimap.upperBound("HDR");
while (i != upperBound) {
    cout << i.value() << endl;
    ++i;
}
 
 
QMultiMap<int, QString> multimap;
multimap.insert(1, "one");
multimap.insert(5, "five");
multimap.insert(5, "five (2)");
multimap.insert(10, "ten");
 
multimap.upperBound(0);      // returns iterator to (1, "one")
multimap.upperBound(1);      // returns iterator to (5, "five")
multimap.upperBound(2);      // returns iterator to (5, "five")
multimap.lowerBound(5);      // returns iterator to (5, "five (2)")
multimap.lowerBound(6);      // returns iterator to (10, "ten")
multimap.upperBound(10);     // returns end()
multimap.upperBound(999);    // returns end()
 
for (auto it = multimap.begin(), end = multimap.end(); i != end; ++i)
    i.value() += 2;
 
void erase()
{
QMultiMap<QString, int> multimap;
QMultiMap<QString, int>::const_iterator i = multimap.cbegin();
while (i != multimap.cend()) {
    if (i.value() > 10)
        i = multimap.erase(i);
    else
        ++i;
}
erase_if(multimap, [](const QMultiMap<QString, int>::iterator it) { return it.value() > 10; });
}
 
 
if (i.key() == "Hello")
    i.value() = "Bonjour";
 
 
QMultiMap<QString, int> multi;
multimap.insert("January", 1);
multimap.insert("February", 2);
...
multimap.insert("December", 12);
 
for (auto i = multimap.cbegin(), end = multimap.cend(); i != end; ++i)
    cout << qPrintable(i.key()) << ": " << i.value() << endl;
 
 
QMultiMap<QString, int> map1, map2, map3;
 
map1.insert("plenty", 100);
map1.insert("plenty", 2000);
// map1.size() == 2
 
map2.insert("plenty", 5000);
// map2.size() == 1
 
map3 = map1 + map2;
// map3.size() == 3
 
for (auto it = multimap.cbegin(), end = multimap.cend(); it != end; ++it) {
    cout << "The key: " << it.key() << endl
    cout << "The value: " << qPrintable(it.value()) << endl;
    cout << "Also the value: " << qPrintable(*it) << endl;
}
 
// Inefficient, keys() is expensive
QList<int> keys = multimap.keys();
int numPrimes = std::count_if(multimap.cbegin(), multimap.cend(), isPrimeNumber);
qDeleteAll(multimap2.keys());
 
// Efficient, no memory allocation needed
int numPrimes = std::count_if(multimap.keyBegin(), multimap.keyEnd(), isPrimeNumber);
qDeleteAll(multimap2.keyBegin(), multimap2.keyEnd());
 
QMultiMap<QString, int> map;
map.insert("January", 1);
map.insert("February", 2);
// ...
map.insert("December", 12);
 
for (auto [key, value] : map.asKeyValueRange()) {
    cout << qPrintable(key) << ": " << value << endl;
    --value; // convert to JS month indexing
}