Re: calculating length of an substring

brasilino@xxxxxxxxx wrote:
Hi Folks:

I'm trying to calculating a substring length directly from pointer
address, like this:

char *e = NULL, *s = NULL;
int len = 0;

s = strchr (url,'.');
e = strrchr (url,'?');
len = (int) s - e;
^^^^^
Not only is a cast unneeded, it introduces an error into your program.
You are trying to subtract a pointer from an int.


Since 's' and 'e' are pointers, I think that's can be make a math
over it, like 's++'.

But your subtraction is a pointer from an int, not a pointer from a pointer. If you _must_ use an unneccesary cast, use
len = (int)(s - e);
but that means exactly the same thing as the cast-less
len = s - e;

Using gcc 4.1.2 (on glibc 2.6 and Linux 2.6.23) it points the
following error:

"error: invalid operands to binary -"

And that is obviously true.
.

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