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Difference between constant pointer and pointer to constant ?

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chose

posted Sep 1, 2014 by Neelam

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2 Answers

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Constant pointer : It means the pointer itself is constant i.e you can't point this pointer to some other variable.

A constant pointer is defined as : type * const pointer_name;

Lets see the example.

int main()
{
    int val1 = 10, val2 =  20;
    int * const ptr = &val1;
    /* "int * const ptr" this is called a  constant pointer. */
    ptr = &val2; 
    /* This line will produce error.  Because ptr is a constant pointer and hence can't point to another variable. */
    printf("%d\n",  *ptr);
    return 0;
}

Pointer to constant : can change the address they point to but cannot change the value kept at those address.

 A pointer to constant is defined as :    const type * pointer_name;

Lets see the example.

int main()

    int val = 10;
    const int * ptr = &val;
    /* "const int * ptr" this is called a pointer to  constant. */
    *ptr = 10; 
    /* This line will produce error.  Because ptr is a pointer to constant and hence can't change the value */ 
    printf("%d\n",  *ptr);
    return 0;
}
answer Sep 2, 2014 by Arshad Khan
0 votes

Constant pointer :
Given Pointer is constant, so we cant change the address.

Pointer to constant:
Pointer pointing to the value is constant, so we cant change the value

answer Dec 4, 2014 by sivanraj
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Also can we declare a variable as "constant volatile" ? if yes then what may be the possible reason to do so?

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int arr[ ] = { 1, 2 };
p = arr; /* p is pointing to arr */

How pointer p will behave ?

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