QMap: Iterator and foreach

ALLINXXX

Hi.
Here's my code;

#include <QCoreApplication>
#include <Qdebug>
#include <QMap>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    QMap<int,QString> Employee;

    Employee.insert(1,"Bob");
    Employee.insert(2,"Chad");
    Employee.insert(3,"Marry");
    Employee.insertMulti(1,"Amy");

    foreach(int i, Employee.keys())
    {
        qDebug() << Employee[i];
    }

    QMapIterator<int,QString> Iter(Employee);
    while(Iter.hasNext())
    {
        Iter.next();
        qDebug() << Iter.key() << Iter.value();
    }

    return a.exec();
}

But the result is :
"Amy"
"Amy"
"Chad"
"Marry"

1 "Amy"
1 "Bob"
2 "Chad"
3 "Marry"

So my question is:
Why the results of "foreach" and "Iterator" is differet????
I mean,why foreach makes two "Amy"??

Thanks for helping !

Paul Colby

Hi @ALLINXXX, welcome :)

Employee.insert(1,"Bob");
Employee.insertMulti(1,"Amy")

Here you have two items under the key 1, so Employee.keys() returns 1 twice as per the docs:

Keys that occur multiple times in the map (because items were inserted with insertMulti(), or unite() was used) also occur multiple times in the list.

So then this line executes twice with i set to 1.

qDebug() << Employee[i];

Both times the [] operator just returns the last value associated with the key 1, as per the docs:

If the map contains multiple items with key key, this function returns a reference to the most recently inserted value.

Cheers.

ALLINXXX

@Paul-Colby
Appreciate!
One one Question ,How to turn "UNSOLVED" question to solved question
thanks! (^o^)/

kshegunov

@ALLINXXX
Take a look here: http://forum.qt.io/topic/62700/hitchhiker-s-visual-guide-to-the-qt-forum

ALLINXXX

@kshegunov
Thanks!
The forum is nice for rookies!

elishajoseph

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