What is the real difference between Pointers and References?

Question

AKA - What\'s this obsession with pointers?

Having only really used modern, object oriented languages like ActionScript, Java and C#, I don\'t really understand the

Answer 1

Also just something to note, you can use pointers in C# (as opposed to normal references) by marking a block of code as unsafe. Then you can run around changing memory addresses directly and do pointer arithmetic and all that fun stuff. It's great for very fast image manipulation (the only place I personally have used it).

As far as I know Java and ActionScript don't support unsafe code and pointers.

Answer 2

If you haven't seen pointers before, you're surely missing out on this mini-gem:

void strcpy(char *dest, char *src)
{    
        while(*dest++ = *src++);
}

Answer 3

To be honest, most seasoned developers will have a laugh (hopefully friendly) if you don't know pointers. At my previous Job we had two new hires last year (just graduated) that didn't know about pointers, and that alone was the topic of conversation with them for about a week. No one could believe how someone could graduate without knowing pointers...

Answer 4

I use pointers and references heavily in my day to day work...in managed code (C#, Java) and unmanaged (C++, C). I learned about how to deal with pointers and what they are by the master himself...[Binky!!][1] Nothing else needs to be said ;)

The difference between a pointer and reference is this. A pointer is an address to some block of memory. It can be rewritten or in other words, reassigned to some other block of memory. A reference is simply a renaming of some object. It can only be assigned once! Once it is assigned to an object, it cannot be assigned to another. A reference is not an address, it is another name for the variable. Check out C++ FAQ for more on this.

Link1

LInk2

Answer 5

Pointers are for directly manipulating the contents of memory.

It's up to you whether you think this is a good thing to do, but it's the basis of how anything gets done in C or assembler.

High-level languages hide pointers behind the scenes: for example a reference in Java is implemented as a pointer in almost any JVM you'll come across, which is why it's called NullPointerException rather than NullReferenceException. But it doesn't let the programmer directly access the memory address it points to, and it can't be modified to take a value other than the address of an object of the correct type. So it doesn't offer the same power (and responsibility) that pointers in low-level languages do.

[Edit: this is an answer to the question 'what's this obsession with pointers?'. All I've compared is assembler/C-style pointers with Java references. The question title has since changed: had I set out to answer the new question I might have mentioned references in languages other than Java]

Answer 6

Programming in languages like C and C++ you are much closer to the "metal". Pointers hold a memory location where your variables, data, functions etc. live. You can pass a pointer around instead of passing by value (copying your variables and data).

There are two things that are difficult with pointers:

1. Pointers on pointers, addressing, etc. can get very cryptic. It leads to errors, and it is hard to read.
2. Memory that pointers point to is often allocated from the heap, which means you are responsible for releasing that memory. Bigger your application gets, harder it is to keep up with this requirement, and you end up with memory leaks that are hard to track down.

You could compare pointer behavior to how Java objects are passed around, with the exception that in Java you do not have to worry about freeing the memory as this is handled by garbage collection. This way you get the good things about pointers but do not have to deal with the negatives. You can still get memory leaks in Java of course if you do not de-reference your objects but that is a different matter.