How to create a dictionary in Qt

Comments

13 Sep
2009

Article Review by deepikagohil (20090913)

Qt is a cross-platform application development framework, which is widely used for developing GUI application. Qt has portability for desktops and embedded systems. Appication in Qt adds high efficiency and high run-time performance on our device.

This article merely represents an application to create simple dictionary in Qt. It has made two applications for a dictionary by using QHash and QMap APIs. Both have similar functionalities. The article gives detailed description, code snippest and screensot for the applications.

The article is in organized manner and it will help beginners to learn QHash and QMap APIs in Qt for Symbian.

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This code snippet demonstrates how to create a dictionary of key/value pairs in Qt. The QHash class is a template class that provides a hash-table-based dictionary that provides very fast lookup of the value associated with a key.

QHash provides very similar functionality to QMap. Both are used to create a dictionary.

Article Metadata

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Tested with

Devices(s): Emulator

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Compatibility

Platform(s): S60 3rd Edition FP1, S60 3rd Edition FP2, S60 5th Edition

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Platform Security

Signing Required: Self-Signed

Capabilities: None

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Article

Keywords: QHash,QMap

Created: james1980 (12 Jan 2009)

Last edited: hamishwillee (11 Oct 2012)

Preconditions

• Download and install the Qt SDK

Various Function of QHash class

• Returns the value associated with the key.

QHash<QString, int> hash;

• To look up a value, use operator[]() or value():

int num1 = hash["thirteen"];
int num2 = hash.value("thirteen");

• Normally, a QHash allows only one value per key. If you call insert() with a key that already exists in the QHash, the previous value is erased. For example:

hash.insert("plenty", 100);
hash.insert("plenty", 2000);
// hash.value("plenty") == 2000

Source File

#include <QHash>
#include <QLabel>
#include <QtGui>
#include <QApplication>
#include <QString>
#include <QHBoxLayout>
#include <QWidget>
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QHash<QString, int> hash;
    QWidget win;
    QHBoxLayout *layout = new QHBoxLayout;
    hash["one"] = 1;
    hash["three"] = 3;
    hash["seven"] = 7;
    hash.insert("twelve", 12);
    QLabel *label1=new QLabel;
    int num2=2;
    int num1 = hash.value("one");
    if (hash.contains("three"))         // Checks in the hash table, Return the value if it exist
         num2 = hash.value("three");
    int num3 = hash["seven"];
    int x = hash.value("thirty", 30);    // If "thirty" is not there in a hash table than assign 30 to x.
    QString str1;
    str1.setNum(num1);
    label1->setText(str1);
    layout->addWidget(label1);
    win.setLayout(layout);
    win.show();
    return a.exec();
}

Similar is with QMap

QHash provides very similar functionality to QMap. The differences are:

• QHash provides faster lookups than QMap. (See Algorithmic Complexity for details.)
• When iterating over a QMap, the items are always sorted by key. With QHash, the items are arbitrarily ordered.
• The key type of a QMap must provide operator<(). The key type of a QHash must provide operator==() and a global qHash(Key) function.

Source code

#include "Qdict.h"
 
#include <QtGui>
#include <QApplication>
#include <QHash>
#include<QMap>
#include <QLabel>
#include <QString>
#include <QHBoxLayout>
#include <QWidget>
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QMap<QString, int> map;
       QWidget win;
       QHBoxLayout *layout = new QHBoxLayout;
       map["one"] = 1;
       map["three"] = 3;
       map["seven"] = 7;
       map.insert("twelve", 12);
       QLabel *label1=new QLabel;
       int num2=2;
       int num1 = map.value("one");
       if (map.contains("three"))         // Checks in the hash table, Return the value if it exist
            num2 = map.value("three");
       int num3 = map["seven"];
       int x = map.value("thirty", 30);    // If "thirty" is not there in a hash table than assign 30 to x.
       QString str1;
       str1.setNum(num1);
       label1->setText(str1);
       layout->addWidget(label1);
       win.setLayout(layout);
       win.show();
 
    return a.exec();
}