Re: hash_map : what is wrong?

"Giovanni Dicanio" <>
Tue, 27 May 2008 15:57:48 +0200
"K?r?at" <> ha scritto nel messaggio

The code below sometimes results access violation at hash_map::erase :

char * popItem (int nKey)
     char * item = NULL;

     stdext::hash_map <int, char * >::iterator hmIterator =
m_hmItemMap.find (nKey);

It seems that you did follow-up neither Brian nor me.

However, I still believe that if you use std::string instead of raw char*
pointers, you will have no access violation.

You may consider the following simple example code, which uses std::string
instead of char* (I renamed your popItem() method as Extract()):


#include <hash_map>
#include <string>

class IntToString

    void Insert( int key, const std::string & value )
        typedef std::pair< int, std::string > IntStringPair;

        m_map.insert( IntStringPair( key, value ) );

    std::string Extract( int key )
        std::string item;

        IntToStringMap::iterator it = m_map.find( key );
        if ( it != m_map.end() )
            item = it->second;

            m_map.erase( key );
            // Not in map: throw an exception
            throw std::invalid_argument( "Key not presenet in map." );

        return item;

    // ...
    // ... other members
    // ...


    typedef stdext::hash_map< int, std::string > IntToStringMap;
    IntToStringMap m_map;


Test like this:


IntToString map;
map.Insert( 1, "January" );
map.Insert( 2, "February" );
map.Insert( 5, "May" );

cout << map.Extract(5) << endl;
cout << map.Extract(1) << endl;
cout << map.Extract(2) << endl;



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