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From: Roy.Browning@f506.n106.z1.fidonet.org (Roy Browning)
Newsgroups: comp.lang.c++
Subject: Passing function pointers in C++
Message-ID: <5115.25805AED@urchin.fidonet.org>
Date: 8 Dec 89 19:04:45 GMT
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 > From: abbott@aerospace.aero.org (Russell J. Abbott)
 > Date: 1 Dec 89 16:30:44 GMT
 > Organization: The Aerospace Corporation, El Segundo, CA
 > Message-ID: <62298@aerospace.AERO.ORG>
 > Newsgroups: comp.object,comp.lang.c++
 > 
 > In article <32106@watmath.waterloo.edu> gjditchfield@watmsg.waterloo.edu 
 > (Glen Ditchfield) writes:
 > >  ...   In practice, in C++, wouldn't it be simpler to pass a comparison
 > >function as an argument to the sort() function?
 > 
 > Can you really do that in C++?  What would the declarations look like?
 > That would be even more flexible than the generic sort that I asked
 > about originally.

Russell:

        Yes you can pass function pointers in C++, an edited version of the syntax is listed below.  Also if you wish to look at some very simple code call my system and download DL_2.ZIP.  Personally I believe that deriving different sorting methods from the base class is much cleaner and more in line with OOP.

                         Migrating from C to C++,

                           Roy Browning

HEADER

        extern "C" {
                    typedef int (*CMP)(const void **,const void **);

                    extern int Cmp_FileName(const struct FIND **p1,
                                            const struct FIND **p2);
                    ....
                    ....

                   };

        class FileList {

               ....;
               ....;

        public:

             FileList(const char *name = "*.*",
                      const int attrib = zero,
                      CMP func = NULL);
             ....;
             ....;

        };

DEFINITION

        static FileList::FileList(const char *name,
                                  const int attrib,
                                  CMP func)
        {
             ....;
             ....;
        
            if (func)
                  qsort(F,num_files,sizeof(struct FIND *), func);
        }

TEST

        main()
        {
             FileList test5("*.*",FA_DIREC | FA_HIDDEN, Cmp_FileSize);

             ....;
             ....;
        }