In C++ is it a good practice to use 'this'?

Question

I was wondering if it was a good practice to use 'this' in C++. At first I thought I should be because that way you make obvious that the thing you are referring is a member of the current class but sometimes you end with code like:

Document::Document(QWidget *parent) : QWidget(parent)
{
    this->file = 0;
    this->layout = new QGridLayout(this);
    this->layout->setSpacing(2);
    this->layout->setMargin(0);
    this->setLayout(this.layout);
    this->textArea = new QTextEdit(this);
    this->textArea->setLineWrapMode(QTextEdit::NoWrap);
    this->textArea->setAcceptDrops(true);
    this->textArea->setAcceptRichText(true);
    this->textArea->setUndoRedoEnabled(true);
    this->textArea->setFont(QFont("Mono" , 11));
    this->layout->addWidget(this->textArea);
    this->textArea->show();
    this->textArea->setFocus();
}

I thing this would look a lot better without all the 'this' specially when it is used like this->layout->addWidget(this.textArea);. And I think the code should use the same style in most cases to make it easier to be read so, should I use 'this' just when it is necessary or is it a good practice to use it to make clear that you are referencing a member of the same class.

Answer 1

There's no single answer to this. It depends on the context, and it depends on who you ask.

Some people use this all the time. Some never use it. Some instead rename all member variables with a special prefix (mFile instead of file).

I prefer to only use the this prefix when it's necessary to avoid ambiguity.

In well written code, it is usually obvious whether you're referring to a local or a member variable, and so this doesn't really do much. But sometimes it can be hard for the reader to determine if a variable is a class member or not. Then this is a good way to clarify.

Answer 2

If using this makes it easier to read (easier to understand, that is) then the extra typing is well worth the effort.

In a complex program every line of code will be written once but read many times (and by different programmers), so it's a good investment.

One of the most readable languages I know, Python, forces you to write self.x (the equivalent of this->x of C++) every single time and that is not an issue at all. The problem with it is that in Python when you write slef.x instead of self.x the error is caught at runtime, but this is a different unrelated issue...