What does `const T * const` mean?

Question

I read an example C ++ template, and part of the template signature confused me.

I am reading this correctly:

const T* const foo; 

Is foo a const* up to a const T ?

Answer 1

Yes, this is a constant pointer to the constant T Ie, you can neither change the pointer, nor what it points to.

const T* forbid you to change everything that the pointer indicates, but allows you (within the language) to check the value in *(foo+1) and *(foo-1) . Use this form when you pass pointers to immutable arrays (for example, the C string you only have to read).

T * const means that you can change the value of T pointed to by foo , but you cannot change the pointer itself; therefore you cannot say foo++; (*foo)++ foo++; (*foo)++ , because the first statement will increment (change) the pointer.

T * will give you complete freedom: you get a pointer to an array, and you can check and modify any member of this array.

Answer 2

Yes, foo is a constant pointer to the constant T.

Answer 3

Yes; this is exactly what it means.

Since there is always little confusion about const when using pointers, the following possibilities are possible:

• const T * aConstant

  means aConstant - variable pointer on constant T

• T const * aConstant

  does the same thing.

• T * const aConstant

  declares that aConstant is a constant pointer and

• T const * const aConstant (or const T * const aConstant )

  declares a constant constant T pointer constant T

Answer 4

This is const-pointer-const-const. Therefore, if T was int, then the array is a pointer to int, which is const in two ways:

pointer-to-const: the value that the pointer points to cannot be changed (or points to const int) const: the memory address stored in the pointer cannot change

It is also the same as T const * const array

See the wiki on const correctness .

Answer 5

Yes, it is, I think the name var (const) is what haunts you.

Answer 6

Yes.

---

 const T* 

does const array elements ... at least with respect to foo .

 foo[0] = T(); // Illegal! foo[1] = T(); // Illegal! foo[2] = whatever; // Illegal! 

---

 const 

makes foo constant pointer. Therefore it is illegal:

 foo = &some_array; 

---

Variable

 foo 

... if you do not know what it is, you should seriously consider attending preschool.

Answer 7

Yes, it just means that you not only cannot change what foo points out, but you also cannot change the value of foo itself to point to some other instance of T