1. Lab 2 main issues
Point and line classes should NOT have their own protected “type” attributes
these hide the parent (shape) classes attribute with the same name
Fall 2004
CS-321 Dr. Mark L. Hornick

2. Lab 2 main issues
Point and line operator=() shouldn’t copy serial number attribute
Serial numbers should be unique
Point and line copy constructor doesn’t copy “type” attribute
Base class copy constructor not automatically called
Fall 2004
CS-321 Dr. Mark L. Hornick

3. Lab 2 main issues
Image destructor does not call delete the shapes in the collection or clear the vector/list
memory leaks
Just call Erase()
Fall 2004
CS-321 Dr. Mark L. Hornick

4. Lab 2 main issues
Clear() -ing the shape collection in image::operator=, Erase(), or destructor, but not deleting the objects
memory leaks
Fall 2004
CS-321 Dr. Mark L. Hornick

5. Lab 2 main issues Shallow copies
Image copy constructor
Image::operator=()
Just copying pointers to shapes results in multiple references to the same shape!
Fall 2004
CS-321 Dr. Mark L. Hornick

6. Lab 2 main issues Assignment operator=… No check for self-assignment
Assignment should replace previous, not append
Fall 2004
CS-321 Dr. Mark L. Hornick

7. Don’t assign over yourself!
operator= Example
Employee& Employee::operator=(const Employee& rhs) {
if (this != &rhs) {
age = rhs.age; …; }
return *this;
Don’t assign over yourself!
Fall 2004
CS-321 Dr. Mark L. Hornick

8. Debugging your programs in Linux
What causes segmentation faults?
How do you find the source of a segmentation fault?
Fall 2004
CS-321 Dr. Mark L. Hornick

9. Steps to solving segmentation faults
Modify your .pro file to build a debug version of your program
…and link the Electric Fence shared library into your program during the link step
Run your program from within the GNU debugger (gdb)
Fall 2004
CS-321 Dr. Mark L. Hornick

10. Electric Fence A runtime head memory monitor
Download Electric Fence (free)
Unzip to someplace on you filesystem
Remake the project
make clean
make
This builds the shared library libefence.so
Fall 2004
CS-321 Dr. Mark L. Hornick

11. Add the following lines to your .pro file…
#CONFIG += qt warn_on release thread #original
CONFIG += qt warn_on debug thread
#add library to linker’s search path
unix:LIBS += =L/home/hornick/cs321/efence/electric-fence / -lefence
Fall 2004
CS-321 Dr. Mark L. Hornick

12. Debugging with gdb Use Adept Package Manager to install gdb
Run gdb – get gdb prompt
file <file> - loads your executable file into gdb
run - starts your program
bt - backtrace – a stack dump with line numbers
quit - exit gdb
Fix problem located by gdb/electric fence
Fall 2004
CS-321 Dr. Mark L. Hornick