c++ program has triggered a breakpoint on operator[]

Question

I'm creating class Student, and I'm getting an error: program has triggered a breakpoint on operator[]. Please help me and show what's wrong, and what is missing.

Fixed:

#include "stdafx.h"
#include <iostream>

class Student {
public:
    Student();
    ~Student();
    void Show();
private:
    char* Name;
    char* Surname;
    char* DateOfBirth;
    unsigned long PhoneNumber;
};

Student::Student() {
    Name = nullptr;
    Surname = nullptr;
    DateOfBirth = nullptr;
}

Student::~Student() {
    if (Name != nullptr) delete[] Name;
    if (Surname != nullptr) delete[] Surname;
    if (DateOfBirth != nullptr) delete[] DateOfBirth;
}

void Student::Show() {
    std::cout << Name << " " << Surname << "\t" << DateOfBirth << "\t" << PhoneNumber << std::endl;
}

class StudentGroup {
public:
    StudentGroup();
    ~StudentGroup();
    void Add(char* Name, char* Surname, char* DateOfBirth, unsigned long PhoneNumber);
    Student& operator[](int index); 
private:
    Student* stud;
    int length;
};

StudentGroup::StudentGroup() {
    length = 0;
    stud=nullptr;
}

StudentGroup::~StudentGroup() {
    delete[] stud;

}

void StudentGroup::Add(char* Name, char* Surname, char* DateOfBirth, unsigned long PhoneNumber)
{
    Student* stud1; 
    stud1 = new Student[length+1];
    for (int i = 0; i < length; i++)
        stud1[i] = stud[i];
    delete [] stud;
    stud = stud1;   
    stud[length].SetName(Name);
    stud[length].SetSurname(Surname);
    stud[length].SetDateOfBirth(DateOfBirth);
    stud[length].SetPhoneNumber(PhoneNumber);
    length++;
}

Student& StudentGroup::operator[](int index) {
    return stud[index];
}

int _tmain(int argc, _TCHAR* argv[])
{
    setlocale(LC_CTYPE,"Russian");
    StudentGroup students;
    students.Add("Ivan","Ivanov","2010-01-01",234234422);
    students.Add("Petr","Petrov","2012-01-01",365753663);
    students[0].Show();
    return 0;
}

***Please help me and show what's wrong*** You probably need to spend some time and debug so that you can tell us what you think is wrong. — drescherjm, Jan 18 '21 at 21:10
Your constructor is faulty in that it does not initialize `stud` to a nullptr. — drescherjm, Jan 18 '21 at 21:13
Short answer: undefined behavior. I see how it invokes it in (at least) 2 different ways, in `StudentGroup::AddStudent`. — Algirdas Preidžius, Jan 18 '21 at 21:14
Relieve yourself of memory allocation issue and use `std::string`. — Thomas Matthews, Jan 18 '21 at 21:59
See https://stackoverflow.com/questions/4193982/delete-a-pointer-to-pointer-as-array-of-arrays , It makes good approach to deal with pointer object that has pointers, deletion mechanism! — Ali Razmkhah, Jan 18 '21 at 22:10
What debugging details it is needed? It doesn't show any breakpoint. — jsmith, Jan 19 '21 at 13:14

score 1 · Answer 1 · answered Jan 18 '21 at 21:34

1

drescherjm is correct in the comments.

Your constructor doesn't initialize StudentGroup::stud, so when you attempt to increase the size of it you call delete [] <uninitialized_pointer>.

To fix this, you should have:

StudentGroup::StudentGroup() {
    stud = nullptr;
    length = 0;
    nextIndex = 0;
}

answered Jan 18 '21 at 21:34

Bill Lynch

80,138
16
128
173

Did you test it before posting? if true, which platform or compiler you used? – Ali Razmkhah Jan 18 '21 at 21:36
@AliRazmkhah: Whatever repl.it uses and gdb. – Bill Lynch Jan 18 '21 at 21:54
Hi, this does not help, error is in `operator[]` – jsmith Jan 19 '21 at 13:16

score 0 · Accepted Answer · answered Jan 18 '21 at 21:22

0

You struct student has pointers, exactly 3 pointers!

It is obvious calling delete[] stud; without handling deletion of char* Name, char* Surname and char* DateOfBirth members of each student object, leads to HEAP CORRUPTION ERROR

answered Jan 18 '21 at 21:22

Ali Razmkhah

280
1
10

This would lead to a memory leak, but I don't see how this would lead to a corruption of the heap. – Bill Lynch Jan 18 '21 at 21:26
Very Simple! Run the code! heap corruption error appeared! In vs 2017 c++11! – Ali Razmkhah Jan 18 '21 at 21:29
And please tell me, deletion of pointer object that has some pointer members (array) that are initiated by "new" operator leads only memory leak??? nor Heap corruption?? – Ali Razmkhah Jan 18 '21 at 21:31
Thank you, but error is in `operator[]`. What's wrong here? – jsmith Jan 19 '21 at 13:12
Please see above comments, in vs 2017 c++11 as adding second student and "delete[] stud" called I encountered "HEAP corruption error" – Ali Razmkhah Jan 19 '21 at 13:53
Sorry, I changed many things. I have edited the code. – jsmith Jan 19 '21 at 14:01
Added fixed code to the question. – jsmith Jan 19 '21 at 14:50

c++ program has triggered a breakpoint on operator[]

2 Answers2