C++ Simple Pointer mistake can't figure out why?

Question

I am trying to design a StudentReviewSystem, which simply has courses, students, etc. Now, I am trying to add a course object to the courses array. Since, I am doing it dynamically; when I insert a new course, I copy the olders to new array and insert new one. However, when I delete the older array it gives me invalid pointer error. I cannot figure out why? Thanks for help.

void StudentReviewSystem::addCourse(int courseId, string courseName) {
    //increment number of courses
    setNumCourses(numCourses + 1);
    Course* newCourses = new Course[numCourses];

    if (courses != NULL) {
        // copy courses to new one
        for (int i = 0; i < numCourses - 1; i++) {
            newCourses[i].setCourseId(courses[i].getCourseId());
            newCourses[i].setCourseName(courses[i].getCourseName());
        }

        // delete old courses
        delete courses;
    }

    newCourses[numCourses - 1].setCourseId(courseId);
    newCourses[numCourses - 1].setCourseName(courseName);
    courses = newCourses;
}

This is courses class.

#include "Course.h"
Course::Course() {
}

Course::~Course() {
}

int Course::getCourseId() const {
    return courseId;
}

void Course::setCourseId(int courseId2) {
    courseId = courseId2;
}

string Course::getCourseName() const {
    return courseName;
}

void Course::setCourseName(string courseName2) {
    courseName = string(courseName2);
}

And this is the main.

int main() {
    StudentReviewSystem srs;

    srs.addCourse(111, "foo");

    srs.addCourse(222, "foo");

    srs.addCourse(333, "foo");

    srs.addCourse(444, "foo");

    return 0;
}

Do yourself a favour if you're using C++ and check out `std::vector<>` which will take this pain away from you. — Moo-Juice, Nov 21 '13 at 13:00
possible duplicate of [deleting dynamic array in c++](http://stackoverflow.com/questions/20101172/deleting-dynamic-array-in-c) — Roddy, Nov 21 '13 at 13:00
`delete courses;` may not call your destructors. If `courses` is an array, use ` delete [] courses;`. — Johan, Nov 21 '13 at 13:01
Just search for "StudentReviewSystem" here and you'll find your homework has already been done. — Roddy, Nov 21 '13 at 13:01
@Roddy: I guess StackOverflow is also TeachingAssistantOverflow? ;-) — Joe Z, Nov 21 '13 at 13:03

score 2 · Accepted Answer · answered Nov 21 '13 at 13:01

2

I think you forgot something: delete [] courses; actually deletes the array - you were only deleting the pointer.

answered Nov 21 '13 at 13:01

Eutherpy

4,471
7
40
64

score 1 · Answer 2 · answered Nov 21 '13 at 13:02

1

This isn't an answer to your problem, but I'd like to show you could do this with the standard library. One way is std::map, one is std::vector.

I suggest a map:

#include <map>
#include <string>
std::map<int, string> courses;

To add a course:

courses[111] = "foo";

Number of courses:

courses.size();

Or you could use std::vector instead.

#include <vector>
std::vector<Course> courses;

To add:

courses.push_back(Course(111, "foo"));

Number of courses look the same as with map.

answered Nov 21 '13 at 13:02

dutt

7,909
11
52
85

Thanks for your suggestions but i need to do this in that way. – memn Nov 21 '13 at 13:12
It seems that OP doesn't need "always-sorted". if so, using `std::vector<>` is much better for performance. – ikh Feb 25 '14 at 01:14

C++ Simple Pointer mistake can't figure out why?

2 Answers2