Re: How to avoid CMapStringToPtr sorting ?

From:

"Giovanni Dicanio" <giovanni.dicanio@invalid.it>

Newsgroups:

microsoft.public.vc.mfc

Date:

Thu, 25 Oct 2007 10:56:44 +0200

Message-ID:

<#R7TRUuFIHA.1388@TK2MSFTNGP05.phx.gbl>

"Abin" <abintom@gmail.com> ha scritto nel messaggio
news:1193296581.109638.84450@v23g2000prn.googlegroups.com...

CMapStringToOb m_myMap;
m_myMap.SetAt("CCC",0);
m_myMap.SetAt("ZEE",0);
m_myMap.SetAt("ABB",0);

POSITION pPos = m_myMap.GetStartPosition();
CString strName;
CObject *pObj;
while (pPos != NULL)
{
m_myMap.GetNextAssoc(pPos, strName, pObj);
AfxMessageBox(strName);
}
<<<<<<<<<
When i iterate the keys i get "ZEE", "ABB" followed by "CCC".

Is there any way to retrieve the keys in same order of insertion.

For what I know: no, if you only use map.

I think you should use both a map and a vector (or linked list). The map
stores the association string key -> ptr, and the vector stores information
about key insertion order.

So, when you add a new key to the map, you also add this key to the vector.
And you retrieve the keys in insertion order, looping for each vector item.

(This is what I suggested in the above post.)

This is a sample code, to show what I mean (I'm sorry, but I prefer using
STL containers like std::vector and std::map and not MFC containers - also
note that STL containers work well with CString, which is a well-designed
string class for Windows development, better than std::string/wstring,
IMHO):

<code>

//
// MAIN TEST
//
void CTestOrderMapDlg::OnBnClickedRunTest()
{
    typedef std::vector< CString > StringList;
    typedef std::map< CString, Person * > Persons;

    StringList names;
    Persons persons;

    //
    // Add some objects to the collection (map).
    // Also add the key to the key list, so we can retrieve
    // that in the same order of insertion.
    //

    persons[ _T("Bob") ] = new Person( _T("Bob"), 40 );
    names.push_back( _T("Bob" ) );

    persons[ _T("Mike") ] = new Person( _T("Mike"), 70 );
    names.push_back( _T("Mike" ) );

    persons[ _T("Jeff") ] = new Person( _T("Jeff"), 28 );
    names.push_back( _T("Jeff" ) );

    //
    // Print content in insertion order
    //
    Clear();
    StringList::const_iterator it;
    for ( it = names.begin(); it != names.end(); ++it )
    {
        WriteLine( persons[ *it ]->ToString() );
    }

    //
    // Clear objects
    //
    for ( it = names.begin(); it != names.end(); ++it )
    {
        Person * person = persons[ *it ];
        delete person;
        persons[ *it ] = NULL;
    }
    persons.clear();
    names.clear();
}

</code>

These are the other code blocks required by the above code (m_lstOutput is a
CListBox):

<code>

//
// Test class to be stored in the map
//
class Person
{
public:
    Person()
        : Age(0)
    {
    }

    explicit Person( LPCTSTR name, int age )
        : Name( name ), Age( age )
    {
    }

    CString ToString() const
    {
        CString s;
        s.Format( _T("%s (%d years old)"), Name, Age );
        return s;
    }

    CString Name;
    int Age;
};

// Clear the output list-box
void CTestOrderMapDlg::Clear()
{
    m_lstOutput.ResetContent();
}

// Add a new line to the output list-box
void CTestOrderMapDlg::WriteLine( LPCTSTR line )
{
    ASSERT( line != NULL );
    m_lstOutput.AddString( line );
}

</code>

Giovanni