Thread: sorting using pointer to pointer not working

  1. #16
    Registered User
    Join Date
    Sep 2008
    I can't believe this.

    I am using Code::Blocks 8.02.
    I added
    to the watch window, just as I did before every time. It displays the member structures, and it still shows garbage for the member struct values except for r_pt_by_SeqNum[0], which is correct.

    BUT adding a watch specifically for a single struct like this
    for any i shows the correct value for the sorted member variable seq_num.

    So the code seems to work, but what I am telling Code::Blocks to watch is wrong.
    Watching *r_pt_by_SeqNum shows all structures, but with wrong values.

    thank you, thank you, thank you!

  2. #17
    Algorithm Dissector iMalc's Avatar
    Join Date
    Dec 2005
    New Zealand
    I still wasn't able to spot the error in your code that makes it sort incorrectly. However I would suggest trying to reproduce the problem with the minimum number of items possible, and then step through the code and see what it is doing.
    Oh wait it was working afterall? Ah no wonder I couldn't find the bug.

    Btw, When you're using integer keys and have lots of them, perhaps a few thousand, then FlashSort beats MergeSort. However if you do look into that, beware of the bugs in the version on You may want to copy the code from my website instead, see my sig.
    RadixSort is another good popular one for when there are a large number of items, but FlashSort is simpler yet more tweakable with regards to the memory usage vs speed tradeoff.
    Or if you want to stick to comparison based techniques, IntroSort is about as good as you can get in the general case.
    My homepage
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  3. #18
    Registered User
    Join Date
    Sep 2008

    Sorting using pointer to pointer not working - SOLVED

    Thank you all for helping.
    And a big thank you again to tabstop for making me actually look at the values themselves instead of relying blindly on what the IDE showed me.

    To sum it up:

    1. The routine was working all along.

    2. I instructed Code::Blocks to watch
    as an array, and it did in fact list the structure array, but with wrong values, except for structure[0]. So I assumed a was seeing the right thing (the array), and that the routine was not working.

    3. tabstop's post resolved the issue: I listed each array[i]->seq_num, and lo and behold, they had the right values.

    4. So I either instructed Code::Blocks incorrectly about what to show, or this is a bug in Code::Blocks. It did list the structures of the array, but did not resolve what the individual pointers in the array pointed to, except for array item[0].

    Now I can get on with the program.
    Thank you all.

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