Question

The question is as in the title.

For example:

QPropertyAnimation *animation;
animation = new QPropertyAnimation(this, "windowOpacity", this);

or

QPropertyAnimation animation;
animation.setTargetObject(this);
animation.setPropertyName("windowOpacity");
animation.setParent(this);

Which is more efficient?

edit: though it has no significant difference unless done repeatedly, i would still like to know, i would rather want answers than opinions -as stackoverflow’s guidelines suggest.

Answer 1

First, why new in the first example? I’ll assume that you will create both variables on the same storage (heap / stack).

Second, this isn’t a matter of Qt, it applies to C++ in general.

Without any prior knowledge about the class you are creating, you can be sure of one thing: The constructor with arguments version is at least as efficient as the setter version.

This is because, in the worst case, the constructor might look like this:

QPropertyAnimation(QObject* target, const QByteArray & prop_name, QObject* parent = 0)
{
  // members are default initializer, now explicitly set
  this->setTargetObject(target);
  this->setPropertyName(prop_name);
  this->setParent(parent)
}

However, any person that has atleast worked through a good book will write the constructor like this:

QPropertyAnimation(QObject* target, const QByteArray & prop_name, QObject* parent = 0)
  : m_target(target)
  , m_prop_name(prop_name)
  , m_parent(parent)
{
  // members explicitly initialized
}