Question

My coding practice using Qt can best be described as follows:

1. If the Widget is going to be actively used (e.g. A QLineEdit which provides text), I declare it in the header file and then initialise it in MainWindow.cpp.
   e.g. TextEditor.h:

class TextEditor
{
//other code
private:
QLineEdit edtFind;
};

2.. If a widget is not going to be used (e.g. QLabel, QWidget), or it’s part of a signal slot system (e.g. QPushButton), I declare and inialise it inside constructor using new.

-e.g.

TextEditor::TextEditor()
{
   //other code
   QWidget* searchPanel = new QWidget();
   edtFind = new QLineEdit("Enter Search Term");
   QPushButton* findButton = new QPushButton("Find");
   connect(findButton,SIGNAL(pressed()),this,SLOT(find()));

   ui->statusbar->addPermanentWidget(searchPanel);
}

My question is, am I using an efficient approach in point 2? Would it be better to not allocate memory from the heap?

Thanks.

Answer 1

Your approach is not efficient. You should use heap allocated objects when you actually need them:

• objects that have a longer lifetime
• using a forward declaration in order to avoid including a header file
• holding a reference to an object created elsewhere

Your approach is more complicated without any visible benefit. Heap is known to be slow, and allocating a large number of small objects is known to fragment it (this might not make a difference in your app but it’s still a bad practice).