Posted By: Anonymous
I’m a little bit confused about something. I was under the impression that the correct way of reading a C string with
scanf() went along the lines of
(never mind the possible buffer overflow, it’s just a simple example)
char string; scanf( "%s" , string );
However, the following seems to work too,
scanf( "%s" , &string );
Is this just my compiler (gcc), pure luck, or something else?
An array “decays” into a pointer to its first element, so
scanf("%s", string) is equivalent to
scanf("%s", &string). On the other hand,
scanf("%s", &string) passes a pointer-to-
char, but it points to the same place.
scanf, when processing the tail of its argument list, will try to pull out a
char *. That’s the Right Thing when you’ve passed in
&string, but when you’ve passed in
&string you’re depending on something that the language standard doesn’t guarantee, namely that the pointers
&string — pointers to objects of different types and sizes that start at the same place — are represented the same way.
I don’t believe I’ve ever encountered a system on which that doesn’t work, and in practice you’re probably safe. None the less, it’s wrong, and it could fail on some platforms. (Hypothetical example: a “debugging” implementation that includes type information with every pointer. I think the C implementation on the Symbolics “Lisp Machines” did something like this.)