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Thread: How to check the result returned from an iterator

  1. #1
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    How to check the result returned from an iterator

    Code:
    it = m_CoopTable->m_SparseMap.find(s);
    
    	if (it != NULL) //Error
    	{
    		return false;
    	}
    This gives me compile-time error. it is an iterator to a hash_map
    Thanks
    Jack

  2. #2
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    Re: How to check the result returned from an iterator

    [ Moved thread ]
    Ovidiu
    "When in Rome, do as Romans do."
    My latest articles: http://codexpert.ro/blog/author/ovidiu-cucu/

  3. #3
    Lindley is offline Elite Member Power Poster
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    Re: How to check the result returned from an iterator

    You check against end(), eg, in this case, m_CoopTable->m_SparseMap.end(). This is in the hash_map::find() documentation.

  4. #4
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    Re: How to check the result returned from an iterator

    Hello Lindley,
    Thank you for your help. The info is very useful.
    I have another trouble concerning with the use of hash_maps
    My program crashes at a spot which has a hash_map that the whole map contains a long series of error items
    It is shown as (error) | 0 in the intellisense window. I have cleared it out right at the start of the constructor.
    (error) | 0
    (error) | 0
    (error) | 0
    etc
    Code:
    stdext::hash_map<std::string, CObjects*> m_SparseMap;
    Any more hints?
    Thanks
    Jack

  5. #5
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    Re: How to check the result returned from an iterator

    Quote Originally Posted by lucky6969b View Post
    I have another trouble concerning with the use of hash_maps. My program crashes at a spot which has a hash_map that the whole map contains a long series of error items
    Your program has a bug.

    You can't get an answer by posting just a declaration.

    Regards,

    Paul McKenzie

  6. #6
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    Re: How to check the result returned from an iterator

    Sorry, i know. uninitiailized var. Too careless...

  7. #7
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    Re: How to check the result returned from an iterator

    Code:
    stdext::hash_map<std::string, CObjects*> m_SparseMap;
    Just a mention that putting pointers to objects inside STL containers is not generally a good idea, precisely because you run into problems like uninitialized objects, memory leaks, double free etc. The only (defendable) use for it is when you somehow really need to use inheritance on the objects.
    Get this small utility to do basic syntax highlighting in vBulletin forums (like Codeguru) easily.
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  8. #8
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    Re: How to check the result returned from an iterator

    Quote Originally Posted by Yves M View Post
    Code:
    stdext::hash_map<std::string, CObjects*> m_SparseMap;
    Just a mention that putting pointers to objects inside STL containers is not generally a good idea, precisely because you run into problems like uninitialized objects, memory leaks, double free etc. The only (defendable) use for it is when you somehow really need to use inheritance on the objects.
    Even then, you have no excuse not to make it a vector of unique_ptr, shared_ptr, or just plain use ptr_vector. EDIT: Oh wait, hash_map, not vector... in that case: ptr_unordered_map.
    Last edited by monarch_dodra; February 8th, 2012 at 08:32 AM.
    Is your question related to IO?
    Read this C++ FAQ article at parashift by Marshall Cline. In particular points 1-6.
    It will explain how to correctly deal with IO, how to validate input, and why you shouldn't count on "while(!in.eof())". And it always makes for excellent reading.

  9. #9
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    Re: How to check the result returned from an iterator

    Quote Originally Posted by lucky6969b View Post
    It is shown as (error) | 0 in the intellisense window. I have cleared it out right at the start of the constructor.
    (error) | 0
    (error) | 0
    (error) | 0
    Jack
    Assuming you are using VisualStudio, this might be an issue that you are using the debugger on a release build. My experience is that in a release build the debugger is not able to inspect the content of the STL containers

  10. #10
    Lindley is offline Elite Member Power Poster
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    Re: How to check the result returned from an iterator

    Quote Originally Posted by Richard.J View Post
    Assuming you are using VisualStudio, this might be an issue that you are using the debugger on a release build. My experience is that in a release build the debugger is not able to inspect the content of the STL containers
    If optimization is disabled it should work okay.

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