Re: Why "Access Violent" throw when insert pair object into std::map

"Doug Harrison [MVP]" <>
Sun, 02 Mar 2008 18:38:07 -0600
On Sat, 1 Mar 2008 00:47:48 +0100, "Giovanni Dicanio"
<> wrote:

<> ha scritto nel messaggio

 bool InsertCell(int nSign, CDataCell& objNewCell);

I would use a const reference, like this:

 bool InsertCell( int nSign, const CDataCell & objNewCell )

 std::pair<std::map<int, CDataCell>::iterator, bool> ret =
CDataCell>::value_type(nSign, objNewCell); //throw an error said
"0x000005, Access violent"

I don't like this long type declarations, IMHO they are not very readable.
I would prefer using typedef's to make things simpler and more readable,
like this:

class CADTNode

   // *** Map typedef ***
   typedef std::map< int, CDataCell > CellMapCollection;
   CellMapCollection m_mapCellCollection;

bool CADTNode::Insert( int nSign, const CDataCell & objNewCell )
    // *** Pair Typedef ***
    typedef std::pair< int, CDataCell > CellMapPair;

    // Insert into Map
    m_mapCellCollection.insert( CellMapPair( nSign, objNewCell ) );


As a minor optimization, it's better to use map::value_type than std::pair
or even std::make_pair; it's less error-prone and often shorter to type, as
the correct type for CellMapCollection is:

     typedef std::pair<const int, CDataCell> CellMapPair;

The only reason the original version would work is due to pair's template
ctor, which would convert pair<int, CDataCell> to pair<const int,
CDataCell> when you call insert(). The best approach would thus be:

     typedef CellMapCollection::value_type CellMapPair;

Doug Harrison
Visual C++ MVP

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