Re: Comment on trim string function please


Ben Bacarisse <ben.usenet@xxxxxxxxx> wrote in message
news:87iqvbjbeg.fsf@xxxxxxxxxxxx
"Bill Reid" <hormelfree@xxxxxxxxxxxxxxxx> writes:

<snip>
In any event, does the following win the prize for most efficient
implementation of the presumed requirements of the function?

I think you have a bug.

char *remove_beg_end_non_text(char *text) {
char *beg;
size_t length;

for(beg=text;*beg!='\0';beg++)
if(!isspace(*beg)) break;

I'd guess

for (beg = text; isspace((unsigned char)*beg); beg++);

makes shorter code with some compilers.

Yeah, but does it fly past the terminating null character? I think
you may have out-obfuscated me...

Also, I've not been following why the cast is important here...

length=strlen(beg);

while(length>0)
if(!isspace(*(beg+(--length)))) break;

*(beg+(++length))='\0';

If length never is never decremented (because it was zero after the
initial space scan) then this writes outside the string. It always
helps to walk through what your code does in boundary cases like ""
and " ".

Actually, the "boundary case" for this is the size of array; as long
as it is at least one character bigger than the "string" then this will
always work. But you are correct if you replace the word "string" with
the word "array fully-populated by the string" above.

There are actually only five possible test cases, which all should
ASSUME a "array fully-populated by the string" (which I unfortunately
didn't): spaces before text, spaces after the text, spaces before and
after the text, just spaces, empty string (six if you count the stupidity
of passing NULL). Pass those five (or six) cases, the thing is
perfect...

return beg==text ? text : memmove(text,beg,length+1);
}

Gotta admit, you couldn't reduce the cycles too much on
that, could you? And it could even win a little bonus prize
for obfuscatory conditions like if(!isspace(*(beg+(--length))))...

You might have obscure it even to yourself!

OK, I need to work on a few things to make it the perfect piece
of obscure ruthlessly efficient code...

---
William Ernest Reid



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