12. Pointers

Pointers in C :

Pointers are special kind of variables which stores memory address of another variables.

Syntax of Pointers :

    datatype *variable_name;    or
    datatype *variable_name = value;

Uses of Pointers :

• Manipulate data present at some specific memory address.
• Increases scope of variables.
• Provides multiple names to single variable.
• Provides a way to create arrays in C.
• Dennis Ritche created arrays with help of pointers.
• Pointers are used to manipulate constant variable value.

Memory allocation in case of pointers :

Memory is allocated by Compiler. | Compiler | Memory| |----------|-------- | 16 - BIT | 2 BYTES | | 32 - BIT | 4 BYTES | | 64 - BIT | 8 BYTES |

Example :

int main()
{
    char   * ptr1;
    int    * ptr2;
    float  * ptr3;
    double * ptr4;

    printf("char : %lu, int : %lu, float : %lu, double : %lu\n",
                sizeof(ptr1), sizeof(ptr2), sizeof(ptr3), sizeof(ptr4)
            );

    return 0;
}

Examples of pointers :

    int main(){
        int number = 10;
        int *ptr; // declaration

        ptr = &number; // initialization

        // getting address of variable
        printf("address of number %u\n",&number);

        // accessing value of pointer.
        printf("Value in pointer %u\n",ptr);

        return 0;
    }

De-referencing Pointers :

• Dereferencing is process of getting value stored at some memory location with help of pointers. or

• Dereferencing is process of getting value of a variable by using memory address stored in pointer.

Uses of Dereferencing :

• Dereferencing is Used to read or write data of memory location stored inside pointer.

• Example : int *number = 10; // changes value of number to 10.

Examples of Dereferencing :

    int main(){
        int marks = 10;
        int *ptr = &marks;

        printf("Marks are %d\n", *ptr); // *ptr is dereferencing pointer to marks.

        return 0;
    }