Debug Assertion failed on making copy constructor

Question

I am trying to make a copy constructor because I have a pointer in my class. However, I got runtime error "Debug Assertion failed" and I do not know what to do. I have two classses, MyMatrix and MyImage. I want to write a copy constructor for MyImage, therefore I also write one for MyMatrix.

class MyMatrix{
private:
unsigned _width, _height; 
unsigned char *_data;

public:
MyMatrix(MyMatrix &other);
}

MyMatrix::MyMatrix(MyMatrix &other) {
_width = other._width;
_height = other._height;
_data = new unsigned char[_width*_height];
memcpy(_data, other._data, _width*_height*sizeof(unsigned char));
}

class MyImage {
public:
int _width;
int _height;
MyMatrix _Y; //gray level
}

MyImage::MyImage(MyImage &other) {
_width = other._width;
_height = other._height;

_Y = MyMatrix(other._Y);
}

int main(){
    char *filename = "hw1_images/p1/house.raw"; //some raw image
    int width = 512;
int height = 512;

    //read the image
    MyImage inputImage(filename, width, height, fileMode::CFA);

    //copy the image 
    MyImage test(inputImage);
 return 0;
 }

I got error even if I comment the memcry(). If I use std::cout to display the value of my copy, it is alway 221. Please help me with it. Thank you.

This is not enough code for us to reproduce the error (and at first glance it looks correct). Could you give us a [minimal complete example](http://stackoverflow.com/help/mcve)? — Beta, Sep 07 '15 at 03:45
Definitely would need a repro example. This could be an issue with the destructor, assignment operator (you have this, too - right?), memory corruption, a problem with the default constructor, or something else. — Michael Burr, Sep 07 '15 at 03:50
If you used a vector, the default copy constructor and assignment operator would just work. Also your class wouldn't leak memory anymore.. let C++ work for you. — Neil Kirk, Sep 07 '15 at 04:03

score 0 · Answer 1 · answered Sep 07 '15 at 03:57

If its just matter of crash then you may do something like below.

class MyMatrix{
private:
unsigned _width, _height; 
unsigned char *_data;

public:
    MyMatrix(){
    _width = 2;
    _height = 3;
    _data = new unsigned char[sizeof(unsigned char)];

}
MyMatrix(MyMatrix &other);
};

MyMatrix::MyMatrix(MyMatrix &other) {
_width = other._width;
_height = other._height;
_data = new unsigned char[(_width*_height) + 1];
memcpy(_data, other._data, _width*_height*sizeof(unsigned char));
}

score 0 · Accepted Answer · edited May 23 '17 at 11:58

You are writing _Y = MyMatrix(other._Y);, I expect that you have defined the assignement operator for your Matrix class : MyMatrix & operator(const MyMatrix & other); otherwise the compiler will create a default one for you that just copy your attributes, meaning your pointer will be copied, not the content.

And, as I see that you can manipulate an important size of data and if you have c++11 enabled, I would definitely look at the copy swap idiom : What is the copy-and-swap idiom?

Debug Assertion failed on making copy constructor

2 Answers2