Thread: Purpose of pointers?

Originally posted by Yawgmoth
What exactly are pointers good for? It seems to me like they're the same thing as variables.

Yes pointers are varaible but variable that can point to the address of other varaible .Why is it so use full well one use of pointer in C is pass-by-reference that when you pass a value lets say from main() to a function it is by default passed by value that mean if the function does any change to that varaible that is passed it wont affect the one in main() but using pass-by-reference it will change the value in main().
There are many other uses for pointer and its the back bone of C..

Imagine if you have this structure:

Code:

typedef struct
{
   int Ages[10000000];
   char Names[10000000][1024];
   char Locations[10000000][4096];
}MYSTRUCT;

And you need to pass it to a function for some modification. Then you can:

A) Pass the structure, this means sending ~50 Gb of data.
B) Pass a pointer to it, this means sending 4 bytes of data.

Seems a little faster to send a pointer than the data, right?


Another thing, run this program and compare the results:

Code:

void Modify1(int Var)
{
   Var = 456;
}

void Modify2(int* Var)
{
   *Var = 456;
}

int main()
{
   int MyVar;

   MyVar = 123;
   printf("Before: %d\n", MyVar);
   Modify1(MyVar);
   printf("After: %d\n\n", MyVar);

   MyVar = 123;
   printf("Before: %d\n", MyVar);
   Modify2(&MyVar);
   printf("After: %d\n\n", MyVar);

   return 0;
}

As you see, in 2 you can modify a variable through a function, in 1 you cannot.

Pointers are variables that store memory address, and you can use it to pass variables to functions and modify them...
You can also dynamically allocate memory using malloc() and free() in C, or new and delete in C++
And pointers are very important in WIN32 Programming.

pointers are for many purposes
- without pointers you can not access memory address.
- you can create dynamic array with pointer.
- many data structures need pointer to solve.
- function can't return char[] but it can return char*
- etc.

Originally posted by momo20016
Pointers allow you to keep hold of an adress of a variable or literal.

True literals (IE not string literals) can not be referred to by a pointer because they have no location in memory. They are strictly rvalues.