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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

2 comments:

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.