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QuestionFree memory allocated by std::multimap Pinmemberkhaliloenit4-Oct-12 3:41 
AnswerRe: Free memory allocated by std::multimap Pinmemberpasztorpisti6-Oct-12 16:26 
It might depend on the implementation of the multimap. I checked it long ago but if I remember right your erase() call sets back the allocation to a minimum, identical to the allocation performed by the default ctor of multimap (at least in the SGI stl implementation of Visual C++ I used at the time). Note that even newly created empty std containers have a small piece of memory preallocated and some containers (like std::vector) dont shrink the size of the allocated memory area (capacity) even if you erase items.
 
A trick that seems to reset the allocated memory of any std containers regardless of stl implementation and container type is the following:
typedef std::multimap<int,int> MyMap;
MyMap global_map;
 
void my_func()
{
    // We create a new map instance and we swap its contents with the other "big" container instance.
    // This swap operation replaces the pointers inside the two containers so after the swap() the
    // global_map contains the small newly allocated blocks, and empty_map contains the big mem blocks
    // previously owned by global_map. Note: when empty_map runs out of scope it releases the big block.
    // This trick works with other stl container types too.
    MyMap empty_map;
    empty_map.swap(global_map);
}

AnswerRe: Free memory allocated by std::multimap [modified] PinmemberStephen Hewitt11-Oct-12 22:53 
GeneralRe: Free memory allocated by std::multimap Pinmemberpasztorpisti11-Oct-12 23:53 

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