[cs631apue] Using fts sort functions

[Paul-Anthony Dudzinski]

I guess that is what I am going to have to do...


On Thu, Oct 10, 2013 at 6:51 PM, Tejas @ Stevens <tnadkarn at stevens.edu>wrote:

> Mine may not be as elegant but I just setup separate sort functions for
> each type of sort and an if/else to call one depending on flags. I didn't
> look at any existing ls code because wanted to learn it as I go and built
> it my way.
>
> It works! :)
>
> On Oct 10, 2013, at 6:48 PM, Paul-Anthony Dudzinski <pdudzins at stevens.edu>
> wrote:
>
> Hello all,
> I am currently trying to implement fts sorting for all the sort options we
> need to do for our project. As c is not my first or even third language I
> was hoping someone could help me detangle the pointers going on in this:
>
> So the fts man page say to use it like this:
>
> FTS *fts_open(char * const *path_argv, int options,
>                                              int (*compar)(const FTSENT
> **, const FTSENT **));
>
> and has this to say about it:
> The argument compar() specifies a user-defined function which may be used
> to order the traversal of the hierarchy. It takes two pointers to pointers
> to FTSENT structures as arguments and should return a negative value, zero,
> or a positive value to indicate if the file referenced by its first
> argument comes before, in any order with respect to, or after, the file
> referenced by its second argument.
>
> So from what I can tell from the documentation I am then to write some
> sort of function that returns -1,0,1 as any qsort should.
>
> Being particularly puzzled and not able to get it to pass anything
> correctly I took a look at ls from bsd and saw some interesting things:
>
> The first thing I noticed is that there are two levels to the sort
> functions: (these are the definitions at the top)
>
> static int mastercmp(const FTSENT * const *, const FTSENT * const *);
> static int (*sortfcn)(const FTSENT *, const FTSENT *);
>
> After some logic it picks a sort type (which is *sortfcn ) and it is used
> in fts like this:
> fts_open(argv, options, f_nosort ? NULL : mastercmp)) == NULL)
>
>
> So formost:
> 1. Why the aliasing of the sort function and why do the types not match
> the man page for what fts is expecting?
> 2. Logically what exactly is this type : const FTSENT * const * and why
> was it set up like this?
> 3. Why are the actual sort functions prototyped like (*sortfcn) and named
> differently? Is this some sort of wild card function name replacement?
>
>
>
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