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Program crashes after deleting the pointer



  •       QList<QPair<char,int>> inferenceResult;
          QPair<char,int> *tempInferenceResult;
          qDebug()<<"Inside connectivity function";
          inferenceResult = //Output from some function
        
        qDebug()<<"Inference result in connectivity"<<inferenceResult;
            if(i==0){
                tempInferenceResult = &inferenceResult[0];
                tempInferenceResult->second = 0;
    
                tempInferenceResult = &inferenceResult[2];
                tempInferenceResult->second = 0;
            }
            qDebug()<<"Temp Inference result"<<*tempInferenceResult;
        **delete tempInferenceResult;**
        ----------
    ------line  of codes------
    -----------------------
       
    

    In the above code i am trying to modify the value of list of Qpair using pointer of type QPair;
    My problem is that when i delete the pointer my program crashes;
    There are also other approaches like inferenceResult[0].second = 0 instead of using pointer but i wanted to know the exact problem with the approach and how to resolve.
    Thanks


  • Lifetime Qt Champion

    Hi
    You take a reference to the inline structure of the list.

    QList<QPair<char,int>> inferenceResult;

    Its not pointer to pair, but a pair. Directly.

    then
    tempInferenceResult = &inferenceResult[0];

    Points to the pair In the list. (inside list)

    delete tempInferenceResult; // try to delete something INSIDE the list which
    only list can do in a safe manner.


  • Moderators

    @Kira
    well obviously, tempInferenceResult is not it's own object instance but it references part of the memory of one of your list items.

    By deleting it you invalidate part of the allocated memory of that list item.,



  • Thanks for the explanation


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