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Monday, May 16, 2005

Is ``int* p;'' right or is ``int *p;'' right?

Both are "right" in the sense that both are valid C and C++ and both have exactly the same meaning. As far as the language definitions and the compilers are concerned we could just as well say ``int*p;'' or ``int * p;''

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.

The critical confusion comes (only) when people try to declare several pointers with a single declaration:

 int* p, p1; // probable error: p1 is not an int*
Placing the * closer to the name does not make this kind of error significantly less likely.
 int *p, p1; // probable error?
Declaring one name per declaration minimizes the problem - in particular when we initialize the variables. People are far less likely to write:
 int* p = &i;
int p1 = p; // error: int initialized by int*
And if they do, the compiler will complain. Whenever something can be done in two ways, someone will be confused. Whenever something is a matter of taste, discussions can drag on forever. Stick to one pointer per declaration and always initialize variables and the source of confusion disappears.

Bjarne Stroustrup


Ramesh said...

Forgot to make a comment earlier.

Very refreshing and very good piece. Good old 'C'...ha...

I sure have a lump in throat that I might be too unwilling to use 'C' after these years with Java and its advanced structures.

phoe6 said...

Yeah Ramesh. I think its become a (bad) habit for me which I would like to end it. Starting again and again. So doing something about it.