What is a nonstatic member function?

Question

I am being told that I can't use the 'this' keyword in a class function. I'm coming from c# and i'm used to this working, but the compiler tells me that it can only be used within nonstatic member functions.

D3DXVECTOR3 position;

void Position(D3DXVECTOR3 position)
{
    this.position = position;
}

are you sure it worked in c#? in c#, a 'class function' is called a 'static method', and you cannot use 'this' in those either? — muratgu, Sep 29 '11 at 16:25
yeah I did it all the time to refer to a classes variable in the constructor, or is the constructor different? — Dollarslice, Sep 29 '11 at 16:27
Perhaps you should show the class this method belongs to - that might help clarify what you're doing — Useless, Sep 29 '11 at 16:31

score 19 · Accepted Answer · edited Mar 28 '15 at 08:50

19

this is a pointer containing the address of the object.

D3DXVECTOR3 position;

void YourClassNameHere::Position(D3DXVECTOR3 position)
{
    this->position = position;
}

Should work.

D3DXVECTOR3 position;

void YourClassNameHere::Position(D3DXVECTOR3 position)
{
    (*this).position = position;
}

Should also work.

edited Mar 28 '15 at 08:50

user541686

205,094
128
528
886

answered Sep 29 '11 at 16:24

Pubby

51,882
13
139
180

@AndréCaron Heh, didn't notice. I edited to include MarkB's changes. – Pubby Sep 29 '11 at 16:27
@AndréCaron Except that we don't know that, because he hasn't given us any context. – James Kanze Sep 29 '11 at 16:27

score 16 · Answer 2 · answered Sep 29 '11 at 16:24

In C++ you need to qualify your Position function with the class name:

void YourClassNameHere::Position(D3DXVECTOR3 position)

Also from @Pubby8's answer this is a pointer, not a reference so you need to use this->position instead (or consider using parameter names that don't shadow class members - I like using trailing _ on my class members).

Also, C++ doesn't pass by reference by default so if D3DXVECTOR3 is a complicated type you'll be copying a lot of data around. Consider passing it as const D3DXVECTOR3& position instead.

score 4 · Answer 3 · answered Sep 29 '11 at 16:26

Not only is Position a free function (not associated with a class) the way you wrote it, but this is also a pointer, not a reference.

D3DXVECTOR3 position;

void ClassName::Position(D3DXVECTOR3 position)
{
    this->position = position;
}

or, if that's supposed to be a constructor,

ClassName::ClassName(D3DXVECTOR3 p) : position(p)
{
}

What is a nonstatic member function?

3 Answers3