Pointer
i need a pointer on pointers (pun intended). can someone explain to me how to use them and what there purpose is becuase i have read the tutorial about pointers and dont exactly understand why they are needed and i kinda understand how to use them.
thanks alot!
Arrays, functions(passing-by-value/passing-by- reference), and classes are all topics permeated with the use of pointers, and unless you spend the time to study each of those topics thoroughly, you aren't going to fully appreciate the "whys" of pointers, but here is a short explanation:
Their primary purpose is efficiency. If you pass an object to a function, the compiler needs to make a copy of the object for the function. Making a copy of an object is terribly inefficient, especially for large objects. In addition, the function can only make changes to the copy it receives, and when the function ends, the copy is destroyed, so the function ends up not being able to make any permanent changes to the original object.
On the other hand, a pointer variable stores a memory address of where the object is located and the address looks something like this:
007E0D50
If you pass a pointer to a function, the compiler copies the pointer and gives the copy to the function, but the effect is very different. First of all, it is very efficient to copy the address since it's so small and therefore it takes almost no time. Also,
the object itself might be extremely massive and take up lots of memory, but the address takes up very little memory. Finally, the function is able to make permanent changes to the original object through a pointer.
Having said all that, it's not necessary to know their purpose to learn the fundamentals of how pointers work. Think of it as a little game. Learn the game, and how it works, and after that, you will gain an appreciation of when to use them and why they are so powerful.
Good luck.
Last edited by 7stud; 08-03-2003 at 03:13 PM.
All data is stored in memory at a specific address. So a little char like this
char foo = 'a'
is stored as 97 (the ascii code for a) in a byte of memory.
This byte of memory has an address that the system uses to locate it. The address can be pretty much anything the program is allocated by the operating system (attempting to read/write/execute stuff outside of the space allocated by the operating system can lead to the operating system killing your program and throwing up an error (GPF or Segfault), because you're not allowed to do that).
so lets say this foo's address (&foo) is 600. and we make a pointer to it called bar.
char *bar = &foo
Now bar itself takes up 4 bytes of memory (on a 32-bit system). bar is a pointer. All bar contains is the address of foo, 97. You can pass bar to functions and this allows functions to edit foo (thus avoiding complicated returns).
Pointers are very important, and you'll see and use them alot. Unless you decide to program in java or something.
misinformation is a gift.
Last edited by Brian; 08-03-2003 at 03:10 PM.
thanks for the replies, i didnt fully understand tehm becuase i only have four month of crap prgramming knowledge. i will try to get the most out of ur posts tho.
ok so i kinda still dont understand pointers, but i am going to show u why i dont get it. in the tutorial they give you this code:
Code:#include <iostream.h> int main() { int x; //A normal integer int *pointer; //A pointer to an integer pointer=&x; //Read it, "pointer equals the address of x" cin>>x; //Reads in x cout<<*pointer; //Note the use of the * to output the actual number stored in x }
ok so you see i understand how all this codes works, but the things i still dont get is, well if you look at this it looks like the pointer is only being you to display the value of x in another way, couldnt this just be done easily with out the extra code just by doing:
Code:cout<<x;
Yes, that was just a basic example of how to use pointers, but not really how pointers are used. They're just for efficiency and like the other people here said, are tied in with functions.ok so you see i understand how all this codes works, but the things i still dont get is, well if you look at this it looks like the pointer is only being you to display the value of x in another way, couldnt this just be done easily with out the extra code just by doing
Well, there are a few things wrong with your code:
1) It does not work.
2) It does not work.
3) It does not work.
Hope this helps.
