Revision of Pointers, the short version! from Thu, 13/11/2008 - 12:31pm

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Thu, 13/11/2008 - 12:21pm — AhHatem

A point could point to anything (reference anything), that could be a pointer to an object of a class , a pointer to a structure, a point to int, to char … to anything actually. A managed environment means that your J VM or .net CLR, takes care of a lot of things for you…

this is the declaration, it doesn’t point to anything now… in other languages, if you tried to use this pointer it will throw an exception , in c it wont it will simply get you the value that originally existed in the place you are pointing to… and if you attempted to write to it, you will overwrite someone else’s data or in best cases you will write in a random place where no one knows if it is used or not.

an important usage of the pointer is passing a variable by reference if we have a function as follows: In c an array is a pointer to the first element of the array. The point here is the dynamic allocation... Note: add the lib where the function malloc exist in malloc.h Nothing will happen, we have changed what the pointer “par” points to not what the original array points to…

For this to work, we need to make a pointer to pointer…

That will change the value of ar… Thus we could do the following to the function:

That’s all… my goal was to overview the pointers briefly… you will have some long book in the c to get it all but this is the short version… Thank you.

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Hi, Great work, I

BrokenArrow - 25/11/2008 - 2:06am

Hi,

Great work, I modified it a bit to improve the code formating :)

I had a question though, do we need all the inter-language talk? I find it a bit confusing and distracting.

What do you think ?

Pointers are _NOT_

MSameer - 02/12/2008 - 1:06am

Pointers are _NOT_ references. A pointer is a normal variable but it carries the memory address of another variable. That other variable can be a premitive type (char, int, bool, long, ..) or an aggregate type (Object, structure, array, ...) or a function (pointers to functions).
Java _HAS_NO_POINTERS_. You obtain an object handle but you can't do more.
It's IMPORTANT and considered a best practice to initialize your pointers (Use NULL if you don't yet know what they will point to). Pointers are randomly initialized. If you try to access it without initializing, you can get a SEGV when you read from it and/or write to it. Depending on the random "value" it points to.
pointers are used for multiple reasons. I can't remember all of them:

C has no "pass by reference". You actually pass the memory address by value here (To change the value of a pointer, you need to pass a pointer to a pointer).
Pass by value can be bad if you have a large data structure!
Some data structures can only be passed as pointers.
In C, you can't practically do strings without pointers.
No dynamic memory allocation without pointers.
The array declaaration is a pointer to the 1st element of the array!
Pointers to functions are important also!