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What's the PURPOSE of const pointers?

+4 votes
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What's the purpose of const pointers?

posted Jun 2, 2014 by Khusboo

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2 Answers

+1 vote
 
Best answer

There are two topics related with constant and pointer is -
1. constant pointer
2. pointer to a constant

1. Constant Pointers
A constant pointer is a pointer that cannot change the address its holding. In other words, we can say that once a constant pointer points to a variable then it cannot point to any other variable.

Sample Declaration: int * const ptr;

2. Pointer to a Constant
A pointer through which cannot change the value of variable it points is known as a pointer to constant. These type of pointers can change the address they point to but cannot change the value at that address.

Sample Declaration: const int* ptr;

Sample Code 

int main(void)
{
  {
    int var1 = 0, var2 = 0;
    int *const ptr = &var1;
    ptr = &var2; // Invalid Operation as ptr is a constant pointer
  }
  {
    int var1 = 0;
    const int* ptr = &var1;
    *ptr = 1; // Invalid operation as ptr is pointer to a constant
  }
}

We have a concept of Constant Pointer to a Constant which is mix of two i.e. pointer can not point to another variable neither change the value of the variable it point to.

Sample Declaration: const int* const ptr;

answer Jun 2, 2014 by Salil Agrawal
+1 vote

While writing a program when you are make sure that a pointer is not going to point something else through its life time, better to make it constant so avoid illegal memory access.

answer Jun 2, 2014 by Vimal Kumar Mishra
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