Hi,

theoretically, the advantage of the 2nd version is, that the 1st one
implements a comparison against a constant (which could be an arbitrary
value), and the latter one checks whether the value of the pointed area
zero. Most architectures does the 2nd task more simple than the 1st
one. On the other hand, the compiler may be able to recognize that the
constant mentioned above is zero and *could* optimize the generated code
to achieve the tighter version would produce the 2nd code. But it is not
necessary the case in all situations.

Regards,
Imre

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On Fri, 26 Oct 2001, Dale Botkin wrote:

> > Out of necessity, I continue to study C.
>
> Yeah, me too.
>
> > On page 105 of "The C Programming Language", there are two versons of
> > function strcpy:
> >
> > version 1:
> > void strcpy(char *s, char *t)
> > {
> >     while ((*s = *t) != '\0') {
> >         s++;
> >         t++;
> >     }
> > }
> >
> > version 2:
> > void strcpy(char *s, char *t)
> > {
> >     while ((*s++ = *t++) != '\0') {
> >         ;
> >     }
> > }
> >
> > Before the second version, we read the following statements...
> >
> > "Experienced C programmers would prefer..."
> >
> > My question is, could you explain why it is good to move both the asignment
> > operation and the increment operation into the while test portion?
>
> > Also, what is the logic behind understanding the actual test in the while
> > loop? I can't understand from the syntax exactly what is being compared to
> > '\0'. Is it *s? *t? If so, why?
>
> It's testing (*s++ = *t++) compared to '\0'.  In effect, it copies *t to
> *s then compares to 0, then increments.  But why really would
> "experienced" C programmers like the second form better?  Well, less
> typing...  that's a big plus...  they do the exact same thing, and CCS
> compiles both to the same size.
>
> Dale
>
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>
>

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