Deleting dynamic arrays?

Question

I'm having problems about deleting dynamic arrays in my project.

First appear:

void StudentReviewSystem::addCourse( const int courseId, const string courseName )
{
    int i = findCourse( courseId );

    if ( i == -1 )
    {
        int newNum = numberOfCourses + 1;
        Course *newCourses = new Course[newNum];
        for ( int j = 0; j < numberOfCourses; j++ )
        {
            newCourses[j] = courses[j];
        }
        Course aCourse(courseId, courseName);
        newCourses[numberOfCourses] = aCourse;
        //delete[] courses;
        courses = newCourses;
        numberOfCourses = newNum;
        cout<< "Course "<< courseId <<" has been added."<< endl;
    }
    else
    {
        cout<< "Course "<< courseId <<" has already exist."<< endl;
    }
}

courses is a pointer which was defined in my header. If I comment out the delete line, code works just fine, otherwise, program crashes.

Another appear:

StudentReviewSystem::StudentReviewSystem()
{
    numberOfCourses = 0;
    courses = new Course[0];
}

StudentReviewSystem::~StudentReviewSystem()
{
    //delete[] courses;
}

I know I must delete my dynamic arrays to avoid memory leaks, but whenever my destructor is called, program crashes so I comment out that line too.

Whenever I try to delete a dynamic array, program crashes no matter what I do.

It turned out that you can't delete[] an array with size 0. So, I check for size every time I want to delete an array. But does a 0 size array causes memory leak?

Are you following [the rule of three](http://en.wikipedia.org/wiki/Rule_of_three_%28C++_programming%29)? — juanchopanza, Nov 20 '13 at 16:19
*Aside*: Unless you are required to use `new` and `delete` here, **don't**. `std::vector` is clearly superior to this approach. — Robᵩ, Nov 20 '13 at 16:22
`courses = new Course[0];` ?? Why 0, what do you want to do with an array of size 0 ? — Johan, Nov 20 '13 at 16:27
User will add courses to the system and that number grows. Initially it is 0. — Efe Gürkan, Nov 20 '13 at 19:03

score 2 · Accepted Answer · edited May 23 '17 at 12:28

If your class manages resources, then you usually need a destructor, copy-constructor, and copy-assignment operator, per the Rule of Three. My guess is that you don't have these, so the class has invalid copy semantics: copying it will just copy the pointer, not the dynamic array, leaving two objects both wanting to delete the same array.

Either implement or delete the copy functions, or (better still) don't manage the resources yourself: use std::vector<Course> to do the work for you. You won't need the destructor either if you do that, and addCourse would be much simpler.

score 0 · Answer 2 · answered Nov 20 '13 at 16:25

0

Either you assign one object of type StudentReviewSystem to another object of the same type without explicitly defining the copy assignment operator (or a copy constructor) or the compiler has a bug when a zero length array is allocated.

answered Nov 20 '13 at 16:25

Vlad from Moscow

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Deleting dynamic arrays?

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