Question

What is the difference in the following code:-

 int a;
 int *p;
 p=&a;
 function(p);

and

 int a;
 function(&a);

I was reading a book where sometimes they have used the first code and sometimes the other. Its not a good book though (by a local author).

Will both codes work the same way or is there any difference?

Also is there any difference in terms of efficiency and does it matter that much?

Thanks

Answer 1

As far as I know compiler implements references as pointers. So there should be no difference in performance. But references are more strict and can protect you from making mistakes. For example you can’t rebind references or can’t perform arithmetic with them

Also some people prefere to pass pointers to the function that modify object. For example

void changeVal(int *p)
{
    *p = 10;
}

They say it’s more readable when you see:

   changeVal(&var)

than

changeVal(var);

EDIT

You can think of reference as another name of the object it refers to. So all the changes made to reference are applied to the object. Here is an example:

void foo_copy(int a) //pass by copy
{
    a = 10; //changes copy
}

void foo(int &a) //bass by reference
{ 
     a = 10; //changes passed value
}

void foo(int *a) //pass an adress of a
{
    (*a) = 10; //change a value pointed by a
    a = nullptr; //change a (the pointer). value is not affected
}