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| greg cox
81th Post
 
Occasional Customer
  
|  "Re(2):C++ Pointers"
, posted Mon 15 Apr 09:29
well for a start a pointer is exactly that: a variable that points directly to a memory location, and not the data at that location.
You can tell which ones are pointers because they will have a little star (*) in there... eg:
node * ptr = new node
what does this do? well even if you havent encountered 'node's yet, it is still just another data type, like int, or char. So what this is doing is a) declaring a new variable called "ptr" (which happens to be a pointer, and this pointer can only point to a data type that was mentioned when creating this pointer... so "ptr" can only point to a 'node' in this case)... and b) it finds an unused chunk of memory - and it sets ptr to "point" to the *memory address* of that chunk of memory. (and not the data at that address, remember :) )
and how is this useful exactly?
heh, for a start, it does away with declaring arrays with a fixed length.
Imagine you wanted to write a program that had an array, but, you wanted it to change its size dynamically - ie after you have compiled the program and during the execution of the program itself you could add extra items of data to the end of this new "array" that you were making, or alternatively you could delete off the end of it, delete parts of it, etc.
This is handy because in the other scenario of having to declare in your code somewhere an int (or char,etc) data[x] type of array, here you have to get the program to set aside a whole chunk of memory, 1 piece for each element in the array... not good when you don't know how much of that array you are going to use! :) It's also poor programming style to waste memory for no good reason, so when you use the above example of creating a *linked list* by using *nodes* (the nodes are joined together by having pointers to the next node along)
you have a memory saving and efficient array!
btw I'm sure pointers have other uses but they are mainly used for linking sets of data together :P
*for the above to make a bit more sense, you might need to first learn about structs (they are custom data types), the syntax for using pointers, and keep a lookout for anything on making a linked list (it might have another name though) since this will show you what pointers can really do!
good luck! sorry about the length and no links :|
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