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Re: std::map advocacy

From Michael S <already5chosen@yahoo.com>
Newsgroups comp.lang.c++
Subject Re: std::map advocacy
Date 2024-04-07 19:48 +0300
Organization A noiseless patient Spider
Message-ID <20240407194845.0000218c@yahoo.com> (permalink)
References (8 earlier) <uurm8q$24ka4$1@dont-email.me> <20240407160050.00004370@yahoo.com> <uuu98b$2qou0$1@dont-email.me> <20240407183854.00000797@yahoo.com> <AyzQN.166158$46Te.62838@fx38.iad>

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On Sun, 07 Apr 2024 16:09:04 GMT
scott@slp53.sl.home (Scott Lurndal) wrote:

> Michael S <already5chosen@yahoo.com> writes:
> >On Sun, 7 Apr 2024 16:06:02 +0200
> >David Brown <david.brown@hesbynett.no> wrote:
> >  
> >> 
> >> Different people have different needs from C++, and use different 
> >> features.  If I were programming on a PC, I'd happily use
> >> std::map<> and the like.  But I don't program on PC's, and I don't
> >> use std::map<>.  If I needed something like that, I'd make my own
> >> class that fitted my requirements tightly - a factor of 10
> >> inefficiency is often fine on big systems, but not on the devices
> >> I work with.
> >> 
> >> But that's all fine - use whatever you find useful from the
> >> language.
> >> 
> >>   
> >
> >Factor of 5-10 (mentioned in my other post) is quite rare and mostly
> >applies not to std::map vs custom implementation of RB or AVL tree,
> >but to std::map vs some form of hash, esp. when the nature of the
> >key is such that relatively simple hash function happens to have good
> >collision avoidance properties and when the database is huge, so O(1)
> >vs O(logN) starts to be significant.  
> 
> The biggest problem I have with std::map is that you cannot
> define a compile time map.    For the application where we use
> map, the maps can be quite large (hundreds or thousands of entries)
> and initialization of those maps impacts application startup time
> significantly (several hundred distinct maps).
> 
> We're planning on replacing std::map with a custom class optimized
> to efficiently handle the data (mmap'd disk file generated by
> a python script).  A binary search on the primary key is the likely
> search algorithm.     The maps don't change during application
> execution.
> 

std::map is known to not be the best data structure for static search.
Not too bad, but not the best.

If you have the case where good hash function does not exist (which is 
extremely rare) then in your scenario simple sorted vector + binary
search will likely be 1.5-2 times faster than std::map. Also when both
key and payload are small, vector can be non-trivially more
compact than map.

Nowadays the best structures probably have to take into account cache
hierarchy, so fat nodes are somewhat better than simple binary search,
but that level of advancement should be used only when speed is VERY
important.

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Ain't that beautiful ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-04 20:11 +0200
  Re: Ain't that beautiful ? Michael S <already5chosen@yahoo.com> - 2024-04-04 21:55 +0300
    Re: Ain't that beautiful ? Sam <sam@email-scan.com> - 2024-04-04 20:00 -0400
      Re: Ain't that beautiful ? scott@slp53.sl.home (Scott Lurndal) - 2024-04-05 00:21 +0000
        Re: Ain't that beautiful ? Michael S <already5chosen@yahoo.com> - 2024-04-05 17:44 +0300
          Re: Ain't that beautiful ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-05 17:27 +0200
            Re: Ain't that beautiful ? Michael S <already5chosen@yahoo.com> - 2024-04-05 18:37 +0300
              Re: Ain't that beautiful ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-05 18:04 +0200
                Re: Ain't that beautiful ? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-04-06 15:55 -0700
                Re: Ain't that beautiful ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-07 08:28 +0200
                Re: Ain't that beautiful ? scott@slp53.sl.home (Scott Lurndal) - 2024-04-07 15:51 +0000
                Re: Ain't that beautiful ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-07 19:35 +0200
                Re: Ain't that beautiful ? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-04-07 12:21 -0700
    Re: Ain't that beautiful ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-05 05:05 +0200
      Re: Ain't that beautiful ? Michael S <already5chosen@yahoo.com> - 2024-04-05 17:52 +0300
        Re: Ain't that beautiful ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-05 17:26 +0200
          Re: Ain't that beautiful ? scott@slp53.sl.home (Scott Lurndal) - 2024-04-05 20:00 +0000
            Re: Ain't that beautiful ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-05 22:29 +0200
              Re: Ain't that beautiful ? scott@slp53.sl.home (Scott Lurndal) - 2024-04-05 21:29 +0000
                Re: Ain't that beautiful ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-06 09:06 +0200
                Re: Ain't that beautiful ? Paavo Helde <eesnimi@osa.pri.ee> - 2024-04-06 17:29 +0300
                Re: Ain't that beautiful ? scott@slp53.sl.home (Scott Lurndal) - 2024-04-06 14:56 +0000
                Re: Ain't that beautiful ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-06 18:34 +0200
                Re: Ain't that beautiful ? wij <wyniijj5@gmail.com> - 2024-04-07 03:00 +0800
                Re: Ain't that beautiful ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-07 08:28 +0200
                Re: Ain't that beautiful ? wij <wyniijj5@gmail.com> - 2024-04-08 07:47 +0800
                Re: Ain't that beautiful ? Michael S <already5chosen@yahoo.com> - 2024-04-07 15:25 +0300
                Re: Ain't that beautiful ? Michael S <already5chosen@yahoo.com> - 2024-04-07 16:00 +0300
                Re: Ain't that beautiful ? David Brown <david.brown@hesbynett.no> - 2024-04-07 16:06 +0200
                Re: Ain't that beautiful ? Michael S <already5chosen@yahoo.com> - 2024-04-07 18:37 +0300
                Re: Ain't that beautiful ? scott@slp53.sl.home (Scott Lurndal) - 2024-04-07 15:58 +0000
                Re: Ain't that beautiful ? David Brown <david.brown@hesbynett.no> - 2024-04-07 18:00 +0200
                Re: Ain't that beautiful ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-07 19:38 +0200
                std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-07 18:38 +0300
                Re: std::map advocacy David Brown <david.brown@hesbynett.no> - 2024-04-07 18:06 +0200
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-07 19:35 +0300
                Re: std::map advocacy David Brown <david.brown@hesbynett.no> - 2024-04-08 11:29 +0200
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-08 13:34 +0300
                Re: std::map advocacy wij <wyniijj5@gmail.com> - 2024-04-08 19:18 +0800
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-08 16:32 +0300
                Re: std::map advocacy wij <wyniijj5@gmail.com> - 2024-04-09 08:40 +0800
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-09 12:48 +0300
                Re: std::map advocacy Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-09 13:16 +0200
                Re: std::map advocacy David Brown <david.brown@hesbynett.no> - 2024-04-08 15:30 +0200
                Re: std::map advocacy scott@slp53.sl.home (Scott Lurndal) - 2024-04-08 17:19 +0000
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-09 00:47 +0300
                Re: std::map advocacy scott@slp53.sl.home (Scott Lurndal) - 2024-04-08 23:00 +0000
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-09 02:20 +0300
                Re: std::map advocacy scott@slp53.sl.home (Scott Lurndal) - 2024-04-09 15:22 +0000
                Re: std::map advocacy David Brown <david.brown@hesbynett.no> - 2024-04-09 09:11 +0200
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-09 13:12 +0300
                Re: std::map advocacy David Brown <david.brown@hesbynett.no> - 2024-04-09 15:01 +0200
                Re: std::map advocacy Richard Damon <richard@damon-family.org> - 2024-04-08 07:10 -0400
                Re: std::map advocacy David Brown <david.brown@hesbynett.no> - 2024-04-08 15:45 +0200
                Re: std::map advocacy James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-04-08 19:42 -0400
                Re: std::map advocacy David Brown <david.brown@hesbynett.no> - 2024-04-09 09:45 +0200
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-09 13:27 +0300
                Re: std::map advocacy David Brown <david.brown@hesbynett.no> - 2024-04-09 15:13 +0200
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-09 18:12 +0300
                Re: std::map advocacy David Brown <david.brown@hesbynett.no> - 2024-04-09 18:22 +0200
                Re: std::map advocacy James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-04-10 02:24 -0400
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-11 00:07 +0300
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-11 16:18 +0300
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-11 16:39 +0300
                Re: std::map advocacy Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-11 16:21 +0200
                Re: std::map advocacy Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-11 15:31 +0200
                Re: std::map advocacy wij <wyniijj5@gmail.com> - 2024-04-11 22:40 +0800
                Re: std::map advocacy David Brown <david.brown@hesbynett.no> - 2024-04-11 16:55 +0200
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-11 16:13 +0300
                Re: std::map advocacy Paavo Helde <eesnimi@osa.pri.ee> - 2024-04-11 18:18 +0300
                Re: std::map advocacy David Brown <david.brown@hesbynett.no> - 2024-04-11 09:57 +0200
                Re: std::map advocacy David Brown <david.brown@hesbynett.no> - 2024-04-11 13:47 +0200
                Re: std::map advocacy Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-11 14:04 +0200
                Re: std::map advocacy wij <wyniijj5@gmail.com> - 2024-04-11 19:25 +0800
                Re: std::map advocacy scott@slp53.sl.home (Scott Lurndal) - 2024-04-07 16:09 +0000
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-07 19:48 +0300
                Re: std::map advocacy Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-07 19:45 +0200
                Re: std::map advocacy Paavo Helde <eesnimi@osa.pri.ee> - 2024-04-08 16:37 +0300
                Re: std::map advocacy Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-07 19:44 +0200
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-08 11:15 +0300
                Re: std::map advocacy Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-08 14:09 +0200
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-08 16:26 +0300
                Re: std::map advocacy Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-08 16:54 +0200
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-08 20:52 +0300
                Re: std::map advocacy Michael S <already5chosen@yahoo.com> - 2024-04-09 00:17 +0300
                Re: std::map advocacy Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-09 07:34 +0200
                Re: Ain't that beautiful ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-07 16:39 +0200
                Re: Ain't that beautiful ? Michael S <already5chosen@yahoo.com> - 2024-04-07 18:41 +0300
                Re: Ain't that beautiful ? Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-07 19:36 +0200
                Re: Ain't that beautiful ? Paavo Helde <eesnimi@osa.pri.ee> - 2024-04-07 18:25 +0300

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