Inhertiting QPtrList

[sunil.thaha]

Hi Guys,
I want to save the contents of the QPtrList to the Database.
So Here is what i did

//DataList.h
template <typename  T>
class DataList : public QPtrList< T > {
 
public:
    DataList(){};
    virtual ~DataList(){};
    bool save();
    int lastError() const;
 
private:
    void setLastError( int iError );
 
private:
    int m_iLastError;
};

//DataList.h
template <typename  T>
class DataList : public QPtrList< T > {

public:
    DataList(){};
    virtual ~DataList(){};
    bool save();
    int lastError() const;

private:
    void setLastError( int iError );

private:
    int m_iLastError;
};

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//DataList.cpp
template < typename T >
DataList<T>::DataList()
    :m_iLastError( QueryResult::ErrorNotSet ) {}
 
template < typename T >
bool DataList<T>::save() {
    DEBUG_WHERE();
    for ( T* pDataItem = first(); pDataItem; next() ) {
        bool bOperationFailed = true;
        if( pDataItem->indicator() == DataListItem::Inserted ) {
            bOperationFailed = pDataItem->insert();
 
        } else if( pDataItem->indicator() == DataListItem::Updated ) {
            bOperationFailed = pDataItem->update();
 
        } else if( pDataItem->indicator() == DataListItem::Deleted ) {
            bOperationFailed = pDataItem->remove();
        }
 
        if( bOperationFailed ) {
            setLastError( pDataItem->lastError() );
            return false;
        }
    }
    return true;
}

//DataList.cpp
template < typename T >
DataList<T>::DataList()
    :m_iLastError( QueryResult::ErrorNotSet ) {}

template < typename T >
bool DataList<T>::save() {
    DEBUG_WHERE();
    for ( T* pDataItem = first(); pDataItem; next() ) {
        bool bOperationFailed = true;
        if( pDataItem->indicator() == DataListItem::Inserted ) {
            bOperationFailed = pDataItem->insert();

        } else if( pDataItem->indicator() == DataListItem::Updated ) {
            bOperationFailed = pDataItem->update();

        } else if( pDataItem->indicator() == DataListItem::Deleted ) {
            bOperationFailed = pDataItem->remove();
        }

        if( bOperationFailed ) {
            setLastError( pDataItem->lastError() );
            return false;
        }
    }
    return true;
}

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But g++ gives me the Following Error
BusinessLogic/DataList.cpp: In member function `bool DataList<T>::save()':
BusinessLogic/DataList.cpp:10: error: there are no arguments to `first' that depend on a template parameter, so a declaration of `first' must be available
BusinessLogic/DataList.cpp:10: error: (if you use `-fpermissive', G++ will accept your code, but allowing theuse of an undeclared name is deprecated)
BusinessLogic/DataList.cpp:10: error: there are no arguments to `next' that depend on a template parameter, so a declaration of `next' must be available

Now where I am i going wrong
Please Help

[jacek]

Try:

for ( T* pDataItem = QPtrList< T >::first(); pDataItem; pDataItem = QPtrList< T >::next() ) {
   // ...
}

for ( T* pDataItem = QPtrList< T >::first(); pDataItem; pDataItem = QPtrList< T >::next() ) {
   // ...
}

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[sunil.thaha]

Thanks Jacek,
But where did u refer this ?. Or which c++ book has this explained

[Cesar]

Correct me, if I'm mistaken, but this code

//DataList.h
template <typename  T>
class DataList : public QPtrList< T > {
 
public:
    DataList(){};
    // [Skip]
};

//DataList.h
template <typename  T>
class DataList : public QPtrList< T > {

public:
    DataList(){};
    // [Skip]
};

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//DataList.cpp
template < typename T >
DataList<T>::DataList()
    :m_iLastError( QueryResult::ErrorNotSet ) {}
//[Skip]

//DataList.cpp
template < typename T >
DataList<T>::DataList()
    :m_iLastError( QueryResult::ErrorNotSet ) {}
//[Skip]

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should lead to link error, as Datalist<T>::Datalist() is implemented twice: both in header and in .cpp files. I suggest something like this:

//DataList.h
template <typename  T>
class DataList : public QPtrList< T > {
public:
    DataList();
    // [Skip]
};
 
//DataList.cpp
template < typename T >
DataList<T>::DataList() :
    QPtrList<T>(), 
    m_iLastError( QueryResult::ErrorNotSet )
{
}
//[Skip]

//DataList.h
template <typename  T>
class DataList : public QPtrList< T > {
public:
    DataList();
    // [Skip]
};

//DataList.cpp
template < typename T >
DataList<T>::DataList() :
    QPtrList<T>(), 
    m_iLastError( QueryResult::ErrorNotSet )
{
}
//[Skip]

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[sunil.thaha]

Correct me, if I'm mistaken, but this code

those Errors were resolved

//DataList.cpp
template < typename T >
DataList<T>::DataList() :
    QPtrList<T>(),
    m_iLastError( QueryResult::ErrorNotSet )
{
}
//[Skip]

//DataList.cpp
template < typename T >
DataList<T>::DataList() :
    QPtrList<T>(),
    m_iLastError( QueryResult::ErrorNotSet )
{
}
//[Skip]

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But do we need to call the Base Constructor Explicity

[Cesar]

But do we need to call the Base Ponter Explicity

Hm... Frankly saying, I'm not sure, anyway that won't hurt . I suppose the behaviour is compiler-dependent, so doing something explicitly should make the code more portable... I guess

[sunil.thaha]

No I don't think so. I have read that When a DErived object is created, the Derived Construtor will call the default constructor of the Base

[jacek]

But where did u refer this ?

I was just using common sense.