Differences between Variables, References and Pointers (C++)

nybbles · n00b Joined: 10 May 2003 Posts: 55 Location: Vancouver

Okay so I'm kinda new to C++... everything so far isnt so bad, apart from being much more convulated than Java. But there is one concept (or maybe two?) that consistently stump me.

Right... here goes.

A variable is a variable. It's just location in memory holding some value.
A pointer is a variable, except it does not hold a value. It holds the memory address to a variable. We use the indirection operator to get that variable, then we can output its value.

Now... a reference, I don't know. Where does the reference lie between a pointer and a normal variable? Also, whats the difference in OOP when returning a Class variable like so

Goalie_Ca · Posted: Sun May 25, 2003 6:35 pm Post subject:

It helps to think like an assembly programmer. Essentially, all those * and & tell the computer is how to interpret the address.

lets let the label var = some address where the variable is to be stored.

var=2
Tell's the computer to store 2 at the memory location where var address'

*var=2
now, you are saying to store 2 where the value of var points to. (ie: not the value of the label, but the address is the value of the memory location where the label points)

&var
tells you the actual value of the label var. ie: the address where var is stored.

With arrays you can address them several ways:
char *p;
*(p+2) == p[2];
p = address of first element in array
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nybbles · n00b Joined: 10 May 2003 Posts: 55 Location: Vancouver

Please answer these questions toooo!!!

maccullt · Posted: Mon May 26, 2003 4:46 am Post subject:

References allow you to have pointer-like behaviour without pointer syntax. In many ways they are a syntactic sugar that makes it easy to write natural looking operator overloading.

Proton · Posted: Mon May 26, 2003 5:38 am Post subject:

Yes, references are great, they are trouble-free pointer arguments or returns. Basically, you can do a whole program passing your classes by value and then try to optimize it simply by putting a few "&" in the arguments and return values!

But this is important! Anything that is passed by reference MUST have a memory address, just like if it was a pointer. So, if you have

fragbert · Posted: Tue May 27, 2003 9:21 am Post subject:

A reference is basically just an alias for an object. When you pass by reference, you are essentially granting the called procedure the use of your variable by a new name (the one in the function declaration). Returning by reference is similar, but you must be careful not to return a reference to a local variable, since the variable is destroyed once the function exits.

References are different than pointers, in that pointers have associated operations (*, ->, etc), and references do not. For more information on pointers, references, etc, I highly recommend "C++ FAQs" by Cline, Lomow, and Girou. It is an invaluable reference (no pun intended

) on all things in C++.