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From: Ioannis Vranos <ivr@remove.this.grad.com>
Newsgroups: comp.lang.ada,comp.lang.c++,comp.realtime,comp.software-eng
Subject: Re: [OT] Re: Teaching new tricks to an old dog (C++ -->Ada)
Date: Tue, 15 Mar 2005 00:47:37 +0200
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Date: 2005-03-15T00:47:37+02:00
List-Id: <comp.lang.ada>

Dr. Adrian Wrigley wrote:

> OK.  How about a trivial but reasonable example:
> 
> #include <time.h>
> #include <map>
> 
> struct interval {
>   tm start, finish;
> };
> 
> int main()
> {
>     std::map<interval, float> hash;
>     interval fred;
> 
>     //   set fred here!    
> 
>     hash[fred] = 0.123;
> }
> 
> No suitable place to put the compare operator!


I am not sure I understood what you are saying. First, map is not using 
hash, so the identifier hash may be misleading.

Secondly you can either specify an operator<, or a predicate like this:


#include <ctime>
#include <map>

struct interval
{
     std::tm start, finish;
};

struct IntervalLessCompare
{
     inline bool operator() (interval a, interval b) const
     {
         using namespace std;

         return difftime( mktime(&a.finish), mktime(&a.start) ) <
                       difftime( mktime(&b.finish), mktime(&b.start) );
     }
};

int main()
{
     using namespace std;

     map<interval, float, IntervalLessCompare> somemap;

     interval fred;

     //   set fred here!

     somemap[fred] = 0.123f;
}








-- 
Ioannis Vranos

http://www23.brinkster.com/noicys