You shouldn't need to use "void ptr + offset to field",
you can cast the void * to be a pointer to whatever
structure you need:
int myCompareFunc(void *p1, void *p2) // I'm leaving off the
// arguments that
*I* still
// need clarified!
{
myStruct *pd1 = (myStruct *) p1;
myStruct *pd2 = (myStruct *) p2;
if (pd1->interesting_field < pd2->interesting_field)
return -1;
...
Of course, if the elements you are comparing are
amenable to mathematical operations, you can do
something like this:
return (int) (pd1->interesting_field - pd2->interesting_field);
This is, of course, assuming that the comparison
only requires <0, 0 or >0 return values. If it
really needs -1, 0, 1 then you need to do the
explicit comparisons & returns.
--
-Richard M. Hartman
[EMAIL PROTECTED]
186,000 mi./sec ... not just a good idea, it's the LAW!
> -----Original Message-----
> From: Michael S. Davis [mailto:[EMAIL PROTECTED]]
> Sent: Monday, March 22, 1999 2:29 PM
> To: '[EMAIL PROTECTED]'
> Subject: RE: Using DmQuickSort ??
>
>
>
> Ok, almost got it. Let's say my compare functions performs
> as follows:
>
> double elem1 // variables within a record
> double elem2 // variables within a record
>
> if(elem1 < elem2){ return -1 };
> if(elem1 == elem2){ return 0 };
> if(elem1 > elem2){ return +1 };
>
> Now my problem is this. this is easy if I declare elem1 and elem2
> but how do I refer to these as part of the record. I know I can get
> a pointer to the data within the record but am not sure how to make
> the comparrison without moving the data. I'd prefer to just refer
> to these doubles, while in DB Record.
>
> Assume fixed length record (all strings same length).
> Record:
> |<--string2-->|<-double1->|<-double2->|<-string2->| just as an example
> ^
> |____ pointer to record data: UInt dataPtr;
>
> Can I just reference these like:
>
> if( *(dataPtr+OffsetToDouble1) < *(dataPtr+OffsetToDouble2) )
> {
> return -1;
> }
>
> Can I do something like this? I think you get my drift. If not
> what is the correct way to compare two doubles within a
> Record, without
> copying them to another location.
>
> Thanks
>
>
> ----------------------------------------------------
> Shoot-to-Win
>
> Protect the 2nd Amendment
> ----------------------------------------------------
>
>
