STL map : How does it free the newed memory?

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Using Maps new is called but no delete is caught..Can anyone explain why is that?? NOt calling erase() causes memory leak or the memory is automatically freed when it goes out of scope.

Posted 18-Feb-12 23:55pm

Member 8576081

Updated 19-Feb-12 3:46am

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Rahul Rajat Singh · Answer 1 · 2012-02-19T03:47:00

Solution 1

Maps use raii tecnique to avoid resource leak. The map never keeps the handle passed to it but insread it uses copy constructor for allocation so that it can independently delete to ensure raii. This is one reason autoptr cant be used with maps.

Posted 19-Feb-12 3:47am

Rahul Rajat Singh

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JackDingler 20-Feb-12 13:35pm

Right, but you should be safe with shared_ptr.

bjorn_ht · Answer 2 · 2012-02-19T09:25:00

STL maps will often allocate a larger chunk of memory and use placement-new to construct contained objects in that memory. Unused memory is then usually kept around and re-used the next time you do an insert. The memory is deleted when the map goes out of scope.

Note that you can supply your own "allocator" template argument class to std::map if you want to study how the map allocates and frees memory.

Member 8576081 · Answer 3 · 2012-02-19T17:38:00

Solution 3

That means even if i dont call erase after insert the memory will be freed automatically as soon as map gets out of scope?

Posted 19-Feb-12 17:38pm