CS2100: Pointers

Pointers

Allows direct manipulation of memory contents

Uses the & operator to refer to the address

e.g:

a = 123

&a = ffbff7dc //they are in hexa

During printf , uses %p as the format specifier for address

A pointer variable is a variable that contains the address of another variable

a_ptr here is a pointer variable and contains the address of variable a

This is like a pointer to the white box

Declaring a pointer

Syntax: type *pointer_name

Assigning a value to a pointer

int a = 123;

int *a_ptr;

a_ptr = &a;

or

int *a_ptr = &a  // declaration

-We use the &(Name of variable) to point to the address where the variable is stored.

- We use *(Name of pointer) to refer to a variable

- We use the (Name of pointer) as a pointer to some variable of the same type

However, only *(Name of pointer) can access the value of the pointer variable

Whatever happened to the pointer will affect the original value

In short, a pointer is a clone of the variable with its memory address stored.

After assigning,

*a_ptr will be the same as a

printf("a = %d\n", *a_ptr);

printf("a = %d\n", a);

Will be the same

Purpose of pointers

- To pass the address of two or more variables to a function so that function can pass back to its caller new values for the variables

- To pass the address of the first element of an array to a function so that the function can access the entire array

Pointers and Functions

Functions will get rid of its data after it has been called, however, we can make use of pointers to ensure that the information retains

Declaration of function:

Void my_fun(int * , int *);

Function:

void my_fun(int *pt_1, int *pt_2){
int temp;
temp = *pt_1;
*pt_1 = *pt_2;
*pt_2 = temp;
}

//this fn swaps

When calling the function from the main, we input:
my_fun(&a,&b)
Assuming that a and b are integers

Use *(Nameofpointer) to change the data
Use (Nameofpointer) to change address
Assign the address using &(variable name)

<Prev 2.C Prog                Next 3. Arrays and Type struct>