On 07/24/11 03:53, Bruno Haible wrote:
> You call it a "wraparound" situation. But there is no arithmetic operation,
> just a cast. Isn't there a better word to denote this situation?
Sorry, I don't know of one. A cast is an arithmetic operation, though,
even though it often has zero runtime cost (in this sense it is like
"n + 0"); so "overflow" and "wraparound" are not inappropriate words here.
> I would leave the
> return (long)offset;
> statement as it is. The code does a conversion, and if the code is more
> explicit about it, the better. Otherwise, when reading the code, I keep
> wondering "what is this if statement good for?", and when searching for
> casts, I have no chance to find it with 'grep'.
I left the cast alone, but still, I don't like it.
It's better to avoid casts when possible, as they can mask
more-important errors, e.g., converting pointers to integers.
Also, conversions happen all the time in C code, and it would
overly clutter the code to mark each one with a cast.
Finally, for this particular case, surely it's obvious
what's going on even without a cast.
I thought of making it even more obvious
by adding a comment, like this:
if (LONG_MIN <= offset && offset <= LONG_MAX)
{
/* Convert offset to the result type 'long', and return. */
return offset;
}
but I dunno, that's uncomfortably close to:
index++; /* Add one to index. */
and clutter like this is best avoided.
How about the following idea instead? It makes the conversion
clearer, and it avoids the cast.
static long
convert_off_t_to_long (off_t n)
{
if (LONG_MIN <= n && n <= LONG_MAX)
return n;
else
{
errno = EOVERFLOW;
return -1;
}
}
long
ftell (FILE *fp)
{
/* Use the replacement ftello function with all its workarounds. */
return convert_off_t_to_long (ftello (fp));
}
