deques, vectors and destructors.

This is a discussion on deques, vectors and destructors. within the C++ Programming forums, part of the General Programming Boards category; Just a quick question, stemming from my previous thread regarding the article about queues: When you 'erase' an element from ...

  1. #1
    Carnivore ('-'v) Hunter2's Avatar
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    deques, vectors and destructors.

    Just a quick question, stemming from my previous thread regarding the article about queues: When you 'erase' an element from a deque (or even vector), is it guaranteed that its destructor will be called immediately, or may the destruction be delayed until the container's internal sequence of elements is reallocated? i.e. if resources are released in the objects' destructors, then there could be unwanted side-effects if there is an indefinite delay before their destruction. I ask, simply because I can't think of an efficient and failsafe way to destroy single elements of an array (assuming that's how deques are implemented), and it would be inefficient to destroy/recreate all elements of the container each time a pop_back() or pop_front() occurs.
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  2. #2
    Registered User Codeplug's Avatar
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    I don't believe the destruction can be delayed.

    Containers that use contiguous memory will use placement new for creation and call destructors explicity.

    gg

  3. #3
    Carnivore ('-'v) Hunter2's Avatar
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    I see. The use of placement new (on a buffer of type unsigned char* I assume), then, is to prevent multiple destructions when the memory needs reallocation?
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    Registered User Codeplug's Avatar
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    Yep, something like that.

    That's also a reason for the varying iterator invalidation rules between container types.

    gg

  5. #5
    Carnivore ('-'v) Hunter2's Avatar
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    Cool, thanks!
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