Why does c++ pointer * associate to the variable declared, not the type?

Question

Why was C++ designed such that the correct way to declare two int *s on the same line is

int *x, *y; 

not

int* x,y; 

I know some people think you should avoid either form and declare every variable on its own line, but I'm interested in why this language decision was made.

Answer 1

To keep compatibility with C code, because that's how C works.

Bjarne makes a good point in his style and technique faq:

The choice between int* p; and int *p; is not about right and wrong, but about style and emphasis. C emphasized expressions; declarations were often considered little more than a necessary evil. C++, on the other hand, has a heavy emphasis on types.

A typical C programmer writes int *p; and explains it *p is what is the int emphasizing syntax, and may point to the C (and C++) declaration grammar to argue for the correctness of the style. Indeed, the * binds to the name p in the grammar.

A typical C++ programmer writes int* p; and explains it p is a pointer to an int emphasizing type. Indeed the type of p is int*. I clearly prefer that emphasis and see it as important for using the more advanced parts of C++ well.

So, the motivation for this working as this in C++ is how it works in C.

The motivation it works like that in C is that, as stated above, C emphasizes expressions rather than types.

Answer 2

The simple answer is: because that's the way C does it. Which, of course, only begs the question: why does C do it this way?

The original philosophy, in early C, is that the declaration be an exact image of the use. So when you write:

int *p; 

, you are declaring that the expression *p has type int (and the compiler works out the actual type of p accordingly).

This, of course, ceased to be true the day C introduced typedef, and later struct. And any resemblance disappeared completely with const (first introduced in C++, then retrofitted into C), where things like

int *const p; 

have no relationship with use. But by then, the die was cast.