Scoping question in C

[Henry Spencer]

On Mon, 13 Jun 2005 billt-lxSQFCZeNF4 at public.gmane.org wrote:
> > If you don't know how long it is, there's really not much you can usefully
> > do with it.  You *have* to have either NUL termination or a known length...
>
> It is possible to count the number of characters until a NUL is found...

*If* you're confident that there is a NUL at the end.  If there isn't one,
it's quite possible for unkind things (e.g. a segmentation-fault trap) to
occur before you happen across a NUL in memory. 

For that matter, even if you do reach an accidental NUL before getting a
trap etc., you could end up with a "string" that happens to overlap the
buffer you're going to copy it into... in which case strcpy() may well
infinite-loop or otherwise misbehave. 

I repeat:  you *have* to have either NUL termination or a known length. 
Somehow you have to know where the sequence of characters ends!

> x=0;
> while ( string[x] != 0 ) { x++; }
> y= malloc(sizeof(char)*(x+1) );
> stcpy (string, y);
> Note there is no guarentee the program is correct or works.

It's not and doesn't. :-)  Should be something like:

	y = malloc(strlen(string) + 1);
	assert(y != NULL);
	strcpy(y, string);

Using strlen() is easier and possibly faster than doing it yourself. 
sizeof(char) is guaranteed to be 1 and hence arguably doesn't need
explicit mention.  A more graceful out-of-memory recovery strategy would
be better than assert(), but *something* needs to check that malloc()
succeeded.  And strcpy() copies from second operand to first, not the
other way.

                                                          Henry Spencer
                                                       henry-lqW1N6Cllo0sV2N9l4h3zg at public.gmane.org

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