Question

I encountered the following problem, and I don’t get any warnings or errors, just a program crash.

When I run in my menu printAll() after dummyData() initialisation. The moment I add one new student it just starts to loop the studentMenu().

Domain.h:

template <class T>
struct Array{
    int length;
    T * M;

    Array( int size ) : length(size), M(new T[size])
    {
    }
    ~Array()
    {
       delete[] M;
    }
};

template <class T>
struct Array{
    int length;
    T * M;

    Array( int size ) : length(size), M(new T[size])
    {
    }
    ~Array()
    {
       delete[] M;
    }
};

template <class T>
void addStudent(int a, int b, std::string c,Array <T> A){
    A.M[a].setStudent(a,b,c);
}

template <class T>
void DummyDataStudents(Array <T> A){
    for(int i=1; i<15; i++){
        A.M[i].setStudent(i, i,"student");
    }
    cout<<"Done Students"<<endl;
}

Controller.h

template <class T>
void _addStudent(Array <T> &A){
    int a,b;
    string c;
    cout<<"Enter ID:"<<endl;
    cin>>a;
    cout<<"Enter Group:"<<endl;
    cin>>b;
    cout<<"Enter Name:"<<endl;
    cin>>c;

    addStudent(a,b,c,A);
}

Student.cpp:

void Student::setStudent(int a,int b,string c){

this->ID = a;
this->group = b;
this->name = c;
}

Menu.cpp:

void Menu::mainMenu(Array <Student> &DBst,Array <Assignment> &DBas){
showMainMenu();
int ret = Menu::intInputHandler();

switch(ret){
case 1:studentMenu(DBst,DBas);break;
case 2:assignmentMenu(DBst,DBas);break;
case 3:statsMenu(DBst,DBas);break;
case 4:_printAll(DBst,DBas);break;
case 0:break;
default:cout<<"Wrong option selected!";break;
}
Menu::mainMenu(DBst,DBas);
}



void Menu::studentMenu(Array <Student> &DBst,Array <Assignment> &DBas){
    showStudentMenu();
    int ret = Menu::intInputHandler();

    switch(ret){
    case 1:_addStudent(DBst);break;
    case 2:break;
    case 3:break;
    case 4:break;
    case 5:_printAllStud(DBst);break;
    case 6:break;
    case 0:mainMenu(DBst,DBas);break;
    default:cout<<"Wrong option selected!";break;
    }
    Menu::studentMenu(DBst,DBas);
}

Main.cpp:

int main(){
//Main function of the program

    DummyDataStudents(DBst);

    DBst.M[10].setStudent(1,10,"sadasd");     //works just fine
    DBst.M[10].printStudent();cout<<endl;

    Menu main;      
    main.mainMenu(DBst,DBas);

    DBst.~Array();
    DBas.~Array();

    return 0;
}

///I think this should be enough to understand. When I add a new student I get loops of menu printing until it crashes; if I call printall() I get a crash directly. Please help and sorry for the long code.

Answer 1

This is a problem:

template <class T> void addStudent(int a, int b, std::string c,Array <T> A){

the Array A is being passed by value, so it is being copied meaning there are now two instances of Array pointing to the same internal array M as there is no copy constructor defined for Array so a default copy constructor is generated. When addStudent() returns the internal array M is being deleted by the instance of Array local to the function. This leaves the remaining instance of Array A with a dangling pointer.

Either implement a copy constructor and assignment operator (which I don’t think you want to do) or make Array non-copyable be declaring the copy constructor and assignment operator private.