Understanding of Pointers and References

**oler1s** · Jun 16 '08, 11:03 PM

Your last block of code is broken. It’s <iostream>, not <iostream.h>. printf is from the C library <cstdio> not <iostream> .

Code:

#include <iostream>

int main()
{
    std::cout << “This is C++”;
}

**Banfa** · Jun 16 '08, 11:14 PM

Generally pointers and references do similar things. In C+ it is considered preferable to use references if possible in large part because it is much much harder (but not impossible) to create an invalid reference than it is to create an invalid pointer.

They are both methods of referring to an object indirectly, a reference is the object where as a pointer is the address of the object. The examples you give are reasonable.

1 important difference is that references must be initialised when the are declared where as pointers do not have to be. However a pointer must be initialised to point to a valid object before it is dereferenced otherwise you will invoke undefined behaviour (which is bad). In fact this ability to declare pointers without initialising them and to have invalid pointers is, I suspect, one of the reasons that references where introduced into C++. It is quite a lot harder to go wrong with a reference than a pointer.

The code tags have changed, the previous code was buggy and holding up site development so it was removed. This is temporary and it will change again so keep putting in the language markers they may be used again someday.

**Nepomuk** · Jun 16 '08, 11:33 PM

Originally posted by oler1s

Your last block of code is broken. It’s <iostream>, not <iostream.h>. printf is from the C library <cstdio> not <iostream> .

Code:

#include <iostream>

int main()
{
    std::cout << “This is C++”;
}

Well, that was supposed to be C instead of C++, as I already used the cpp-tag earlier in my post and wanted to list some different examples. However, I must admit, I didn't check it with the compiler as I only wanted to test, if it would be formatted in this forum. I don't use C normally. But if I just replace "iostream.h " with "cstdio" it compiles fine. (Otherwise the compiler complains, that I'm using out-of-date headers.)
Nevertheless, thank you.

Originally posted by Banfa

Generally pointers and references do similar things. In C+ it is considered preferable to use references if possible in large part because it is much much harder (but not impossible) to create an invalid reference than it is to create an invalid pointer.

That's interesting, as whenever I've seen a C++-Program (even in part) or heard about one, they've nearly always used pointers more than references. (As far as I can remember that is.)
Do these people just have a C background and don't "know better"? Or to reformulate that question: Is "Prefer references!" the opinion of most (good) developers?

Originally posted by Banfa

1 important difference is that references must be initialised when the are declared where as pointers do not have to be. [...] It is quite a lot harder to go wrong with a reference than a pointer.

Makes sense. What advantages do pointers have then? I'm guessing, that Pointer-Arithmethics can't be used in any (reasonable) way with references, can they?

Originally posted by Banfa

The code tags have changed, the previous code was buggy and holding up site development so it was removed. This is temporary and it will change again so keep putting in the language markers they may be used again someday.

Thanks, that's good to know. I'll continue using them. I must say, I preferred coloured and formatted code. :-)

Greetings,
Nepomuk

**Banfa** · Jun 17 '08, 10:01 AM

Originally posted by nepomuk

That's interesting, as whenever I've seen a C++-Program (even in part) or heard about one, they've nearly always used pointers more than references. (As far as I can remember that is.)
Do these people just have a C background and don't "know better"? Or to reformulate that question: Is "Prefer references!" the opinion of most (good) developers?

I'm not sure but I do now that examples in books are often written in a different style to production code. Normally to make the example simpler and easier to understand. User of pointers may be because the author is coming from a C background or because the auther expects the readers to be coming from a C background or because pointers were introduced first with-in the book.

"Prefer references!" is common sense, using something that is more robust rather than something that is less robust is likely to make you code more robust.

Originally posted by nepomuk

Makes sense. What advantages do pointers have then? I'm guessing, that Pointer-Arithmethics can't be used in any (reasonable) way with references, can they?

Pointers have the advantage that you don't need to initialise them when you declare them. This feature is essential for constructs like linked lists, of course you should be using list, map and set STL objects in your code but they have to implement their functionality somehow.

As you point out pointer arithmetic doesn't work on references and for this reason you can not have an array of references but you can have an array of pointers (of course you should be using a vector anyway but it is still easier to create a vector of pointers than a vector of references).

This stems from 2 things. A pointer is an object in it's own right that contains the address of another object. A reference just is the other object, any operation you try on the reference is applied to the object in question.

Pointers are essential if you are going to allocate memory from the heap. They are the only type that hold an address so you will need one to hold the address so you can test to make sure the allocation worked and so you can free the memory when you are finished with it.

Both types have there uses, I tend to stick to the rule of using references for pass data in and out of functions rather than pointers because it cuts down on the need to "check the pointer is valid" at the start of each function. I use pointers in the situations that definately require a pointer rather than a reference.

And of course I would be remiss if I failed to mention that instead of using pointer you can achieve more robust code by using the Handle Design Pattern, article here.

**Nepomuk** · Jun 17 '08, 10:10 AM

Wow Banfa, that's a very informative answer! :-) I'll have a look at that article some time soon, but I guess I'll stick with the basics first. Still got a lot to learn... ^^

Thanks a lot,
Nepomuk

Understanding of Pointers and References

Understanding of Pointers and References

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