Pointer Definition and Declaration

Pointer Definition and Declaration

Pointer is a variable, which holds the address of another variable.

Example: if x contains the address of y, then x is said to “pointing to” y.

Declaration:

Like a variable or a constant, we must declare a pointer before we use it to store a variable address.

Pointer is declared with a preceding asterisk (*).

The general form of a pointer variable declaration is: <data-type> * <var-name>;

Where ‘var-name’ is the name of the pointer variable and ‘data-type’ is a regular ‘C’ data type like int, char etc.

Example:

int *ptr; //Here ptr is the integer pointer variable

int ptr; //Here ptr is the normal integer variable

The declaration tells the compiler three things about the variable ‘ptr’

-Te asterisk (*) tells that the variable ‘ptr’ is a pointer variable.

-‘ptr’ needs a memory location.

-‘ptr’ points to a variable of type ‘data-type’.

Example:

int i=5;

int *ptr; //declare a pointer variable

ptr=&i; //store address of ‘i’ in ‘ptr’

printf(“*ptr=%d\n”,*ptr); //refer to reference of ‘ptr’

Here, ptr is a variable storing an address but not storing the actual value of ‘i’

Pointer Operators

There are two operators that are used with pointers namely, address-of-operator(&) and indirection/de-reference operator(*).

Address-of operator(&): it returns the address of the variable instead of stored value.

“&” is used on a variable (int, char, double and array element) to get the address:

Example: ptr = &j;

Address	Content	Address	Content	Address
1000	i: 40	1001	j: 33	1002
1004	ptr: 1001	1005		1006

“&” cannot be used on a constant, array name, register variable and expressions:

Example:

ip1 =&”abcdef”; //incorrect

ip1 = “abcdef”;  //correct

indirection/De-reference operator (*): It indicates that ptr is a pointer to type int and not a normal variable of type int.

‘*’ is used on a pointer to access the variable it points to.

Example:

int x=1, y ={2,3};

int *ip1, *ip2, *ip3;

ip1 = &x;

*ip1 =0; //x=0

printf(“%d\t%d\n”, x,y[0]);

ip2 =&y[0];

*ip2 = 1; //y[0] = 1;

“* pointer” has a data type which is the same as that of the variable the pointer points to.

int *a;

every pointer points to a specific data type except void *;

void pointer (void *) is used to hold the address of any data type.

Example:

ptr = &j;

*ptr = 99;

Refer to the content of the referee

Address	Content	Address	Content
1000	i: 40	1001	j: 99
1004	ptr: 1001	1005