QApplication limits malloc



  • Hi everyone,

    I've got some problems when I want to dynamically allocate a large array with a QApplication. But the allocation is successfull when I allocate with a QCoreApplication or without Qt at all.

    With QApplication, the second allocation fails :
    @
    int main(int argc, char ** argv)
    {

    double *matriceBrute,*matriceSortie;
    int numberFiles = 1000;
    int nCol = 320;
    int nRow = 240;
    QApplication app(argc,argv);
    matriceBrute = (double*)malloc(nCol*nRow*numberFiles*sizeof(double));
    matriceSortie = (double*)malloc(nCol*nRow*numberFiles*sizeof(double));
    if (matriceBrute == NULL)
        cout << "Matrice Brute failed" << endl;
    else
        cout << "Matrice Brute succeed" << endl;
    if (matriceSortie == NULL)
        cout << "Matrice Sortie failed" << endl;
    else
        cout << "Matrice Sortie succed" << endl;
    

    }
    @

    With QCoreApplication, the two allocations are successful :
    @
    int main(int argc, char ** argv)
    {

    double *matriceBrute,*matriceSortie;
    int numberFiles = 1000;
    int nCol = 320;
    int nRow = 240;
    QCoreApplication app(argc,argv);
    matriceBrute = (double*)malloc(nCol*nRow*numberFiles*sizeof(double));
    matriceSortie = (double*)malloc(nCol*nRow*numberFiles*sizeof(double));
    if (matriceBrute == NULL)
        cout << "Matrice Brute failed" << endl;
    else
        cout << "Matrice Brute succeed" << endl;
    if (matriceSortie == NULL)
        cout << "Matrice Sortie failed" << endl;
    else
        cout << "Matrice Sortie succed" << endl;
    

    }
    @

    And without Qt at all, it's also working :
    @
    int main(int argc, char ** argv)
    {

    double *matriceBrute,*matriceSortie;
    int numberFiles = 1000;
    int nCol = 320;
    int nRow = 240;
    matriceBrute = (double*)malloc(nCol*nRow*numberFiles*sizeof(double));
    matriceSortie = (double*)malloc(nCol*nRow*numberFiles*sizeof(double));
    if (matriceBrute == NULL)
        cout << "Matrice Brute failed" << endl;
    else
        cout << "Matrice Brute succeed" << endl;
    if (matriceSortie == NULL)
        cout << "Matrice Sortie failed" << endl;
    else
        cout << "Matrice Sortie succed" << endl;
    

    }
    @

    Have any idea how I can make it work with QApplication ? By the way, I'm working on Win7 64 bits with Qt Creator mingw 32 bits.

    Thanks.

    Song Chen



  • Hi, What QApplication does is protect you from some serious malpractice! From the OS you only get a limited amount of stack! You try to allocate a very large amount of stack data which probably doesn't fit in that part of memory.
    Using malloc is highly discouraged in C++ and in Qt it's almost forbidden!
    Use the 'new' keyword and put all elements in a QList or QMap! Use Qt containers!! They will be stored in HEAP, not stack. In stack only a list of pointers is kept, so a minimum of stack is required.
    You're not writing C++, your doing C!



  • Well, I tried with new double[] and std::vector and had the same error. But I'm going to look in QList and QMap.

    Thanks


Log in to reply
 

Looks like your connection to Qt Forum was lost, please wait while we try to reconnect.