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MrKBA4-Oct-12 2:41

4-Oct-12 2:41

Hello,

I have the multimap :

TranslationTypeMap  m_TranslationsMap;

where

typedef std::multimap< std::pair<CString, CString>, structTranslationData> TranslationTypeMap;

and

struct structTranslationData
{
    std::wstring wstrTranslationId;
    std::wstring wstrTextTranslated;
};

here an example of insertion in this map:

structTranslationData pstTranslationData;
pstTranslationData.wstrTranslationId = xxxx;            pstTranslationData.wstrTextTranslated = xxxx;     
strIdCaption = yyyy;
strIdLang    = zzzz;            m_TranslationsMap.insert(std::make_pair( std::make_pair(strIdCaption, strIdLang), pstTranslationData ) );

And finaly I write the code below to free memory used by this multimap:

m_TranslationsMap.erase(m_TranslationsMap.begin(), m_TranslationsMap.end());

can we say that memory is free ?
if not , what is the good way to do this ?

Thank you

Re: Free memory allocated by std::multimap

pasztorpisti6-Oct-12 15:26

pasztorpisti

6-Oct-12 15:26

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:

C++

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);
}

Re: Free memory allocated by std::multimap

Stephen Hewitt11-Oct-12 21:53

Stephen Hewitt

11-Oct-12 21:53

Why mix std::strings and MFC CStrings? And yes, the memory used to store the map's contents is freed since the map will handle destructing its contents and the contents don't require any manual cleanup.

Steve

modified 12-Oct-12 4:05am.

Re: Free memory allocated by std::multimap

pasztorpisti11-Oct-12 22:53

pasztorpisti

11-Oct-12 22:53

Well, I didn't assume the question is about freeing memory on destruction because that is trivial, however it might be the OP was curious about that... Smile | :)

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