Pointers

#tutorial11#

Pointers

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Pointers are also variables and play a very important role in C programming language. They are used for several reasons, such as:

• Strings
• Dynamic memory allocation
• Sending function arguments by reference
• Building complicated data structures
• Pointing to functions
• Building special data structures (i.e. Tree, Tries, etc...)

And many more.

What is a pointer?

A pointer is essentially a simple integer variable which holds a memory address that points to a value, instead of holding the actual value itself.
The computer's memory is a sequential store of data, and a pointer points to a specific part of the memory. Our program can use pointers in such a way that the pointers point to a large amount of memory - depending on how much we decide to read from that point on.

Strings as pointers

We've already discussed strings, but now we can dive in a bit deeper and understand what strings in C really are (which are called C-Strings to differentiate them from other strings when mixed with C++)
The following line:

char * name = "John";

Dereferencing

Dereferencing is the act of referring to where the pointer points, 
instead of the memory address. We are already using dereferencing in 
arrays - but we just didn't know it yet. The brackets operator - [0]
 for example, accesses the first item of the array. And since arrays are
 actually pointers, accessing the first item in the array is the same as
 dereferencing a pointer. Dereferencing a pointer is done using the 
asterisk operator *.


If we want to create an array that will point to a different variable in our stack, we can write the following code:


/* define a local variable a */
int a = 1;

/* define a pointer variable, and point it to a using the & operator */
int * pointer_to_a = &a;

printf("The value a is %d\n", a);
printf("The value of a is also %d\n", *pointer_to_a);