Is this correct? (Remove and delete all elements from a STL MAP)

This is a discussion on Is this correct? (Remove and delete all elements from a STL MAP) within the C++ Programming forums, part of the General Programming Boards category; What I want to do is loop through all elements inside the MAP container and then delete it. Lastly, just ...

  1. #1
    Distributed Programming beyonddc's Avatar
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    Is this correct? (Remove and delete all elements from a STL MAP)

    What I want to do is loop through all elements inside the MAP container and then delete it.

    Lastly, just invoke clear() on the map to remove all elements.

    Is my code correct?

    Code:
    MyMap::iterator it;
    
    for (it = MyMap.begin(); it != MyMap.end(); ++it)
    {
        delete (*it).second;
    }
    
    MyMap.clear();
    -dc

  2. #2
    Confused Magos's Avatar
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    Not sure about the *. instead of ->, might work, but this is what I do:
    Code:
    std::map<int>::iterator i;
    
    i = Map.begin();
    while(i != Map.end())
    {
      delete i->second;
      i++;
    }
    
    Map.clear();
    MagosX.com

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  3. #3
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    Is my code correct?
    It's impossible to know without seeing your declaration of your map<>. When you declare an iterator for your map, you have to specify the type of the map<>, and the type of your map depends on what's stored in it, e.g.:
    Code:
    map<string, aClass*> myMap;
    ....
    map<string, aClass*>::iterator i = myMap.begin();
    Not sure about the *. instead of ->
    They are equivalent, but -> is much easier to type.
    Last edited by 7stud; 03-06-2006 at 01:49 PM.

  4. #4
    Distributed Programming beyonddc's Avatar
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    Quote Originally Posted by 7stud
    It's impossible to know without seeing your declaration of your map<>. When you declare an iterator for your map, you have to specify the type of the map<>, and the type of your map depends on what's stored in it, e.g.:
    Code:
    map<string, aClass*> myMap;
    ....
    map<string, aClass*>::iterator i = myMap.begin();
    You're right, it is defined like this...
    Code:
    std::map<std::string, Foo*> MyMap;
    -dc

  5. #5
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    Of course, all the values stored in the map should either be null pointers or pointers to memory allocated with new, and then the code would be ok.

    Technically, it might be considered undefined behavior to have a deleted pointer still stored in the map, but in the real world I wouldn't worry about it.

  6. #6
    semi-colon generator ChaosEngine's Avatar
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    it's also good practice to wrap this kind of usage in a class, so that the destructor will automatically clean up the map.

    [Ignore if you don't like boost]
    Alternatively, use a map of boost.shared_ptr's or a boost.ptr_map which will clean up for you.
    [/Ignore if you don't like boost]
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