How to find specific value in Qmap

Question

I need to know in QMap second value there is. Functions like first() and last() are useless. Do i have to use iterator, some kind of loop?

 QMap<int, QString> map;
 map.insert(1, "Mario");
 map.insert(2, "Ples");
 map.insert(3, "student");
 map.insert(4, "grrr");

eferion · Answer 1 · 2019-03-19T12:28:27.140

14

If you find specific key or value you can do something like this:

// Returns 1
int key1 = map.key( "Mario" );

// returns "student"
QString value3 = map.value( 3 );

or do you want to iterate over all items in QMap?

edited Mar 19 '19 at 12:28

answered Sep 09 '14 at 16:02

eferion

872
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14

score 10 · Answer 2 · edited Dec 18 '18 at 16:42

10

You don't need to iterate over the elements. First get all values via values() and then use contains().

bool ValueExists(const QMap<int, QString> map, const QString valExists) const
{
    return map.contains(valExists);
}

edited Dec 18 '18 at 16:42

jaques-sam

2,578
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answered Sep 10 '14 at 06:50

Ezee

4,214
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1

This will allocate a temporary container for `map.values()`. Just use `map.contains(valExists);` – jaques-sam Dec 18 '18 at 13:50
Regarding the edit to this question: map.values().contains(valueExists) is not the same as map.keys().contains(valueExists). The latter however is equivalent to map.contains(valExists). – Quaternion Nov 03 '21 at 16:49

TheDarkKnight · Accepted Answer · 2017-12-15T09:53:01.610

A map provides quick access based upon the key (the first argument).

So, yes, if you want to know if a value exists (the second argument), you would need to iterate over the map values:-

bool ValueExists(const QMap<int, QString> map, const QString valExists)
{
    QList<QString> valuesList = map.values(); // get a list of all the values
    foreach(QString value, valuesList)
    {
        if(value == valExists)
        {
            return true;
        }
    }
    return false;
}

To simplify the code, we can also use the values' contains() method, which internally will iterate over the values, as above.

How to find specific value in Qmap

3 Answers3