dynamically create QLabels

[jeffmetal]

I am trying to create QLabels's depending on the amount of fields in a give file which will change. The NumFieldsH(hRfmfile) is a c function that that returns the number of fields as an int.

/* Create the data layout */
        dataGroupBox = new QGroupBox;
        gridGroupBox->setTitle(tr("Buttons"));
        datalayout = new QGridLayout;
 
        QLabel field[NumFieldsH(hRfmfile)];
        for(i = 0; i < NumFieldsH(hRfmfile); i++){
 
                field[i] = new QLabel("test");
                datalayout->addWidget(field[i],i,1);
        }
 
        dataGroupBox->setLayout(datalayout);

/* Create the data layout */
        dataGroupBox = new QGroupBox;
        gridGroupBox->setTitle(tr("Buttons"));
        datalayout = new QGridLayout;

        QLabel field[NumFieldsH(hRfmfile)];
        for(i = 0; i < NumFieldsH(hRfmfile); i++){

                field[i] = new QLabel("test");
                datalayout->addWidget(field[i],i,1);
        }

        dataGroupBox->setLayout(datalayout);

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the header

public:
         QGroupBox *dataGroupBox;
         QGridLayout *datalayout;

public:
         QGroupBox *dataGroupBox;
         QGridLayout *datalayout;

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Im getting errors when i compile this for the 2 lines in the loop, what am I doing wrong?

[Santosh Reddy]

QLabel field[NumFieldsH(hRfmfile)];

QLabel field[NumFieldsH(hRfmfile)];

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You are declaring a array of QLabel on stack, when doing so, you need to give a constant value as size.

If you want a variable size array, or don't know the size at compile time, then this is the very reason to use dynamic memory from heap.

Something like this

QList<QLabel *> field;
        int size = NumFieldsH(hRfmfile); // this way NumFieldsH(hRfmfile) is called only once
        for(i = 0; i < size ; i++){ // if NumFieldsH(hRfmfile) is use in for() then it is called for every iteration,which is not good is NumFieldsH(hRfmfile) if trying to read a IO device (file etc)
 
                field.append(new QLabel("test"));
                datalayout->addWidget(field[i], i, 1);
        }

QList<QLabel *> field;
        int size = NumFieldsH(hRfmfile); // this way NumFieldsH(hRfmfile) is called only once
        for(i = 0; i < size ; i++){ // if NumFieldsH(hRfmfile) is use in for() then it is called for every iteration,which is not good is NumFieldsH(hRfmfile) if trying to read a IO device (file etc)

                field.append(new QLabel("test"));
                datalayout->addWidget(field[i], i, 1);
        }

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[wysota]

You forgot to tell us what the errors are.

[stampede]

I'm guessing:

field[i] = new QLabel("test");

field[i] = new QLabel("test");

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: cannot convert 'QLabel *' to 'QLabel' in assignment

datalayout->addWidget(field[i],i,1);

datalayout->addWidget(field[i],i,1);

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: no matching function to call to QGridLayout::addWidget(QLabel,int,int), candidates are QGridLayout::addWidget(QWidget*,int,int)
or something like that
btw. I'm not commenting on solution, because Santosh code should work

----
edit2:

You are declaring a array of (...) on stack, when doing so, you need to give a constant value as size.

Depends on the compiler. For example in g++ 4.5.x following code is perfectly valid:

#include <iostream>
#include <stdlib.h>
 
int main( int argc, char ** argv ){
	if( argc > 1 ){
		int x[ atoi(argv[1]) ];
		std::cout << sizeof(x)/sizeof(int); // should print a value given in program argument
	}
	return 0;
}

#include <iostream>
#include <stdlib.h>

int main( int argc, char ** argv ){
	if( argc > 1 ){
		int x[ atoi(argv[1]) ];
		std::cout << sizeof(x)/sizeof(int); // should print a value given in program argument
	}
	return 0;
}

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This feature is called variable-length arrays (VLA), and is part of C99 standard supported by gcc.

[7ymekk]

QLabel field[NumFieldsH(hRfmfile)];
        for(i = 0; i < NumFieldsH(hRfmfile); i++){
 
                field[i] = new QLabel("test");
                datalayout->addWidget(field[i],i,1);

QLabel field[NumFieldsH(hRfmfile)];
        for(i = 0; i < NumFieldsH(hRfmfile); i++){

                field[i] = new QLabel("test");
                datalayout->addWidget(field[i],i,1);

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I suggest to write it like this:

QLabel* field[NumFieldsH(hRfmfile)];
        for(i = 0; i < NumFieldsH(hRfmfile); i++){
 
                field[i] = new QLabel("test");
                datalayout->addWidget(field[i],i,1);

QLabel* field[NumFieldsH(hRfmfile)];
        for(i = 0; i < NumFieldsH(hRfmfile); i++){

                field[i] = new QLabel("test");
                datalayout->addWidget(field[i],i,1);

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and I'm guessing You're getting non-scalar exception

better way is the Santosh solution, with QList...

[jeffmetal]

thanks you santosh for the help I did it the way you recommended and it worked I also added another row of QlineEdits that i have called data. The problem I am now having is how do I go about setting a new value for the QLineEdits in another method.

I cant seem to access them using data[i].setValue("test"); to work i get the error

/usr/lib64/qt4/include/QtGui/qwidget.h: In member function ‘void Dialog::update()’:
/usr/lib64/qt4/include/QtGui/qwidget.h:672: error: ‘QWidgetData* QWidget::data’ is private
dialog.cpp:234: error: within this context
dialog.cpp:234: error: ‘class QWidgetData’ has no member named ‘setValue’

/usr/lib64/qt4/include/QtGui/qwidget.h: In member function ‘void Dialog::update()’:
/usr/lib64/qt4/include/QtGui/qwidget.h:672: error: ‘QWidgetData* QWidget::data’ is private
dialog.cpp:234: error: within this context
dialog.cpp:234: error: ‘class QWidgetData’ has no member named ‘setValue’

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im assuming this is because the data Lineedits are being declared in the constructor and are out of the scope of my new method.