Re: Comments please

From: Sean Kenwrick (skenwrick_at_hotmail.com)
Date: 01/20/04 

Date: Tue, 20 Jan 2004 21:06:10 +0000 (UTC)

"Sean Kenwrick" <skenwrick@hotmail.com> wrote in message
news:buk4sn$slt$1@sparta.btinternet.com...
>
> "Sean Kenwrick" <skenwrick@hotmail.com> wrote in message
> news:bujv72$olg$1@titan.btinternet.com...
> >
> > "Martin Dickopp" <expires-2004-02-29@zero-based.org> wrote in message
> > news:buj7ok$ka$01$2@news.t-online.com...
> > > "Sean Kenwrick" <skenwrick@hotmail.com> writes:
> > >
> > > > "Jeremy Yallop" <jeremy@jdyallop.freeserve.co.uk> wrote in message
> > > > news:slrnc0omn2.6ih.jeremy@hehe.cl.cam.ac.uk...
> > > > > Christopher Benson-Manica wrote:
> > > > > > This function is intended to print a string guaranteed to be in
> the
> > > > > > form MM/DD/YYYY (assume <stdio.h> and <string.h> are included)
as
> > > > > > YYYY-MM-DD:
> > > > > >
> > > > > > void printdate( const char *date )
> > > > > > {
> > > > > > char tdate[10], *cp;
> > > > > > int mod=10, i;
> > > > > >
> > > > > > cp=tdate;
> > > > > > for( i=6 ; i%mod != 5 ; ++i, ++cp ) {
> > > > > > if( !(i%mod) )
> > > > > > *(cp++)='-';
> > > > > > *cp=date[i%mod];
> > > > > > }
> > > > > > *cp=0;
> > > > > > *strchr( tdate, '/' )='-';
> > > > > > printf( "New date is %s\n", tdate );
> > > > > > }
> > > > >
> > > > > /*
> > > > > This function is intended to print a string guaranteed to be in
> the
> > > > > form MM/DD/YYYY (assume <stdio.h> and <string.h> are included)
as
> > > > > YYYY-MM-DD:
> > > > > */
> > > > > void printdate(const char *date)
> > > > > {
> > > > > printf( "New date is %s-%.2s-%.2s\n", strrchr(date, '/') + 1,
> > date,
> > > > > strchr(date, '/') + 1);
> > > > > }
> > > > >
> > > > > Jeremy.
> > > >
> > > > I like this - very clever - but it relies on 'C' calling convention
of
> > > > passing arguments to functions in reverse order (but so what).
> > >
> > > There is no such convention in C, and the code doesn't make the
> assumption
> > > that there is.
> > >
> > > Martin
> >
> > Doh! Of course your right, I missed the fact that the first call was
to
> > strrchr() rather than strchr() and so I couldn;t quite figure out the
> logic
> > until my brain suggested that the calls must be going in the reverse
order
> > (which still wouldn't work (damn this stupid brain!)).
> >
> > Sean
> >
>
> Actually, I just thought about this again and realised I was right the
first
> time about the C calling convention. Check out this code:
>
>
> #include <stdio.h>
>
> void myfunc(int, int);
>
> int main(){
> int i=0;
> myfunc(++i,i+=8);
> }
>
> void myfunc(int a,int b){
> printf("a=%d b=%d\n",a,b);
> }
>
> Do you think it will print out a=1, b=9 or a=9, b=8 ???
>
> Its the latter, so I should trust my brain a little more !!! (although
I
> agree his solution didn't rely on this calling convention)
>
> Sean
>
>
To illustrate this point some more here is another version that relies on
this C calling convention of
passing arguments in reverse order:

void printdate(char *date)
  {
    printf( "New date is %s-%s-%s\n",
strtok(NULL,"/"),strtok(NULL,"/")-3,strtok(date,"/")+3);
  }

try it, it works!

Sean

Quantcast