destruction of dynamic arrays 1

[pipk]

Dear Friends

Sorry if this is an inane and basic question, it just reflects the ignorance of the writer if it is...

I have created two class files, one for reading Greyscale type pgm files and consists of a dynamically allocated 2 dimensional array. For which the destructor seems to work fine.

My second class file is for reading colour Images and contains 3 greyscale objects (one for each colour channel RGB).

My question is, do i need a separate destructor to remove colour images, or will the grey scale destructor be called automatically?

I currently have a colour image destructor that tries to delete my greyscales (i.e. invoke their destructors) but i am getting a segmentation fault and a core dump.

Once again, sorry if this is a stupid question.

PipK (learner!!)



, the other is a colour image file

 

[mbaranski]

Whenever your greyscale objects go out of scope, the constructor will be called. A good rule of thumb is that if a class contains the statement: new, it needs a corresponding delete for each new.

Therefore, if you have:
ColorImage::ColorImage(){
RGB_I *an_image = new RGB_I();
/* You need to delete the memory */
}

but, with
ColorImage::ColorImage(){
RGB_I an_image = RGB_Init();
}
You don't need one, the destructor for RGB_I will take care of it.

When you get a seg fault, chances are you're deleting something you still need or you're deleting the wrong thing. If you post that, we'll take a look.
Disclaimer:
Beware: Studies have shown that research causes cancer in lab rats.

 

[pipk]

Each member is declared in my header file as:

Grey_Scale *Red; etc

The following is my colourimage constructor:

Colour_Image::Colour_Image(string c, long d, long e, long f)
{
Red = new Grey_Scale("Red", d, e, f);
Green = new Grey_Scale("Green", d, e, f);
Blue = new Grey_Scale("Blue", d, e, f);
}

Each Grey_scale object is an unsigned char**

I have tried the following methods of deletion (more out of frustration than anything else).

Colour_Image::~Colour_Image()
{

delete [] Red; //etc
//This causes seg fault.

delete Red; //etc
//as above.

delete *Red; //etc
// won't compile as it is expecting a //pointer.
}

Hope you can help.

Cheers

pipk

 

[mbaranski]

The 2nd one should work right, have you verified your destructor for greyscale images works correctly, post it here... I think that may be the problem.
Disclaimer:
Beware: Studies have shown that research causes cancer in lab rats.

 

[pipk]

Here is the grey desytructor. I was hoping it cleared out the array by column within row.

Grey_Scale::~Grey_Scale()
{
for(int i = 0; i < height; i++)
for(int j = 0; j < width; j++)
delete[] *(array+j);

delete[] array;
}

 

[pipk]

Actually I think I have sussed it. I should
be doing this instead.

Grey_Scale::~Grey_Scale()
{
for(int j = 0; j < height; j++)
delete[] *(array+j);

delete[] array;
}

It has got rid of the seg fault.
Many thanks for bringing it to my attention though - no wonder you keep making tipster of the week.

cheers

pipk