const int = int const?

Question

For example, is

int const x = 3; 

valid code?

If so, does it mean the same as

const int x = 3; 

?

Answer 1

They are both valid code and they are both equivalent. For a pointer type though they are both valid code but not equivalent.

Declares 2 ints which are constant:

int const x1 = 3; const int x2 = 3; 

Declares a pointer whose data cannot be changed through the pointer:

const int *p = &someInt; 

Declares a pointer who cannot be changed to point to something else:

int * const p = &someInt; 

Answer 2

Yes, they are the same. The rule in C++ is essentially that const applies to the type to its left. However, there's an exception that if you put it on the extreme left of the declaration, it applies to the first part of the type.

For example in int const * you have a pointer to a constant integer. In int * const you have a constant pointer to an integer. You can extrapolate this to pointer to pointers, and the English may get confusing but the principle is the same.

For another dicussion on the merits of doing one over the other, see my question on the subject. If you are curious why most folks use the exception, this FAQ entry of Stroustrup's may be helpful.