QHash compile error

[jiveaxe]

Hi,
in a sample application I have created a class member like this:


QHash<int, QComboBox*> hash;
hash.insert(1, comboBox_1);
hash.insert(2, comboBox_2);
hash.insert(3, comboBox_3);

but during compilation I got the following error:


error: ISO C++ forbids declaration of ‘hash’ with no type
error: expected ‘;’ before ‘.’ token

for every insert function.

What's wrong?

Regards

[marcel]

You cannot use pointers as value types with these structures. Try using QPointers, but I am not sure if it will work.

EDIT: actually it works with pointers too. Could you provide more code, since the problem is there.


Regards

[momesana]

do you have included QHash's headerfile?
#include <QHash>
...
A mere forward declaration won't suffice in this case.

[marcel]

I think you forgot to include QHash in the cpp.

[jiveaxe]

But in the manual (http://doc.trolltech.com/4.3/qhash.html) there is an example concerning the use of contains() and value() and the operator[]() in which is created data like mine:


In general, we recommend that you use contains() and value() rather than operator[]() for looking up a key in a hash. The reason is that operator[]() silently inserts an item into the hash if no item exists with the same key (unless the hash is const). For example, the following code snippet will create 1000 items in memory:

// WRONG
QHash<int, QWidget *> hash;
...
for (int i = 0; i < 1000; ++i) {
if (hash[i] == okButton)
cout << "Found button at index " << i << endl;
}
To avoid this problem, replace hash[i] with hash.value(i) in the code above.


QHash is included.

[jiveaxe]

Here the header file:


#ifndef MAINDIALOG_H
#define MAINDIALOG_H

#include <QDialog>
#include <QHash>

class QComboBox;

class MainDialog: public QDialog
{
Q_OBJECT
public:
MainDialog(QWidget *parent=0);

private:
QComboBox *comboBox_1;
QComboBox *comboBox_2;
QComboBox *comboBox_3;

QHash<int, QComboBox*> hash;
hash.insert(1, comboBox_1);
hash.insert(2, comboBox_2);
hash.insert(3, comboBox_3);
};

#endif

[marcel]

hash.insert(1, comboBox_1);
hash.insert(2, comboBox_2);
hash.insert(3, comboBox_3);
But you cannot do this in the header, in the class declaration.
It has to be in a function.

Regards

[jiveaxe]

You're right; now the program compiles but there is a segmentation fault during execution; here the cpp file:


#include <QtGui>
#include "maindialog.h"

MainDialog::MainDialog(QWidget *parent)
: QDialog(parent)
{
hash.insert(1, comboBox_1);
hash.insert(2, comboBox_2);
hash.insert(3, comboBox_3);

comboBox_1 = new QComboBox;
comboBox_2 = new QComboBox;
comboBox_3 = new QComboBox;

for(int i = 1; i < 4; i++)
for(int j = 0; j < 4; j++)
hash.value(i)->addItem("New Entry");

QVBoxLayout mainLayout;
mainLayout.addWidget(comboBox_1);
mainLayout.addWidget(comboBox_2);
mainLayout.addWidget(comboBox_3);
}

The problem seems the line using hash member.

Bye

[marcel]

You have to instantiate the combos BEFORE adding them to the hash.

Regards

[momesana]

you also should create the layout with new instead of using an object that dies when it reaches the end of the scope of the constructor.

[jiveaxe]

Ops, you're again right.

Thanks