Re: Why "Access Violent" throw when insert pair object into std::map
On Sat, 1 Mar 2008 00:47:48 +0100, "Giovanni Dicanio"
<giovanni.dicanio@invalid.com> wrote:
<phoenix8848@gmail.com> ha scritto nel messaggio
news:afbb2802-ccee-46e7-8f9e-f2bea29a83a9@h11g2000prf.googlegroups.com...
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 =
m_mapCellCollection.insert(std::map<int,
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
{
private:
...
// *** 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