What are the differences between const int*, int * const, and const int * const?

Question

What are the differences between const int*, int * const, and const int * const?

 

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Answer 1

Const usage	Meaning	Description
const int *x;	Pointer to a const int	Value pointed to by x can’t change
int * const x;	Const pointer to an int	x cannot point to a different location.
const int *const x;	Const pointer to a const int	Both the pointer and the value pointed to cannot change.

Answer 2

What are the differences between const int, int * const, and const int * const?*

Two "tricks" that can help:

1. You can swap the const with the data type to move the const to the right
   (a bit of care should be taken not to swap too much :-)
2. Read from right

  const int *
      1. => int const *
      2. => pointer to a const int
      so the pointer "points" to an int that can't be changed

  int * const
      2. => const pointer to int
      so the pointer "points" to an int that can be changed,
      but the pointer can't change

  const int * const
      1. => int const * const
      2. => const pointer to const int
      constant pointer (can't change) points to an int that you can't change

-- Mihai Nita [Microsoft MVP, Visual C++]
http://www.mihai-nita.net
------------------------------------------
Replace year with _ to get the real email

Answer 3

What are the differences between const int*, int * const, and const int * const?

The C++ FAQ Lite has a nice discussion of this:

http://www.parashift.com/c++-faq-lite/const-correctness.html

In particular, question 18.5.

Answer 4

int* - pointer to int
int const * - pointer to const int
int * const - const pointer to int
int const * const - const pointer to const int

Now the first const can be on either side of the type so:

const int * == int const *
const int * const == int const * const

int ** - pointer to pointer to int
int ** const - a const pointer to a pointer to an int
int * const * - a pointer to a const pointer to an int
int const ** - a pointer to a pointer to a const int
int * const * const - a const pointer to a const pointer to an int