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  1. #1
    Join Date
    Jan 2021
    Posts
    6

    Do not understand conditional in for loop

    Hello, I was hoping someone could help me understand the conditional in this for loop:

    Code:
    for (auto i = maps.begin(); i != maps.end(); i++)
        {
          if (&((*i).second) == this)
          {
            assert(!getManager().hasActiveMap());
            ret = ret && getManager().setActiveMap((*i).first);
          }
        }
    what is happening here:

    Code:
    if (&((*i).second) == this)
    is this just asking for the value located at "second" of the index i? If so, could this not just be:

    Code:
    if(&*i.second)
    ?

  2. #2
    VictorN's Avatar
    VictorN is online now Super Moderator Power Poster
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    Re: Do not understand conditional in for loop

    Quote Originally Posted by Circuits View Post
    what is happening here:

    Code:
    if (&((*i).second) == this)
    is this just asking for the value located at "second" of the index i? If so, could this not just be:

    Code:
    if(&*i.second)
    ?
    No.
    just because
    Code:
    (*i).second
    is the same as
    Code:
     i->second
    Besides it is in the most cases easier to use construction like
    Code:
    for (auto& it : maps)
    rather than
    Code:
    for (auto i = maps.begin(); i != maps.end(); i++)
    Victor Nijegorodov

  3. #3
    2kaud's Avatar
    2kaud is online now Super Moderator Power Poster
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    Re: Do not understand conditional in for loop

    You need to consider precedence. . has the highest level and then & (as address). and * (as de-reference). So to have .second you need (*I).

    You could have:

    Code:
    if (&i->second == this)
    as -> has a higher precedence than &
    All advice is offered in good faith only. All my code is tested (unless stated explicitly otherwise) with the latest version of Microsoft Visual Studio (using the supported features of the latest standard) and is offered as examples only - not as production quality. I cannot offer advice regarding any other c/c++ compiler/IDE or incompatibilities with VS. You are ultimately responsible for the effects of your programs and the integrity of the machines they run on. Anything I post, code snippets, advice, etc is licensed as Public Domain https://creativecommons.org/publicdomain/zero/1.0/ and can be used without reference or acknowledgement. Also note that I only provide advice and guidance via the forums - and not via private messages!

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  4. #4
    Join Date
    Jan 2021
    Posts
    6

    Re: Do not understand conditional in for loop

    Would this be equivalent then?

    Code:
    for (auto&& i : maps)
        {
          if (i.second == this)
          {
            assert(!getManager().hasActiveMap());
            ret = ret && getManager().setActiveMap((*i).first);
          }
        }

  5. #5
    VictorN's Avatar
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    Re: Do not understand conditional in for loop

    Quote Originally Posted by Circuits View Post
    Would this be equivalent then?

    Code:
    for (auto&& i : maps)
        {
          if (i.second == this)
          {
            assert(!getManager().hasActiveMap());
            ret = ret && getManager().setActiveMap((*i).first);
          }
        }
    Does it compile???
    Victor Nijegorodov

  6. #6
    Join Date
    Jan 2021
    Posts
    6

    Re: Do not understand conditional in for loop

    Oh, heh no, no it doesn't

    Code:
        for (auto& i : maps)
            {
              if (&i.second == this)
              {
                assert(!getManager().hasActiveMap());
                ret = ret && getManager().setActiveMap((i).first);
              }
            }

  7. #7
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    8,223

    Re: Do not understand conditional in for loop

    Quote Originally Posted by Circuits View Post
    Oh, heh no, no it doesn't
    It doesn't compile? And what the compiler says?
    Ovidiu
    "When in Rome, do as Romans do."
    My latest articles: https://codexpert.ro/blog/

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