DEBUG ASSERTION ERRORS!!

[eejay]

I'm writing a data entry program that for a course to get better practice
using inheritance. Here is the header file:

class Course
{

friend ostream &operator<<(ostream &, const Course &);

public:
// Default Constructor.
Course(char *CourseName = "", char *instructor = "", char * semesterYr =
"");
Course(const Course &); // Copy constructor.
~Course();

const Course & operator=(const Course &);

protected:
char *CourseName;
char *instructor;
char *semesterYr;
};

My .cpp is as follows:

#include
#include
#include "Course.h"
#include

Course::Course(char* n, char* i, char* sy)
{
CourseName = n;
instructor = i;
semesterYr = sy;
}

Course::Course(const Course &objC)
{
CourseName = new char[strlen(objC.CourseName) + 1];
strcpy(CourseName,objC.CourseName);

instructor = new char[strlen(objC.instructor) + 1];
strcpy(instructor,objC.instructor);

semesterYr = new char[strlen(objC.semesterYr) + 1];
strcpy(semesterYr,objC.semesterYr);

}


Course::~Course()
{
delete CourseName, instructor, semesterYr;
}

ostream &operator<<(ostream &out, const Course &right)
{
out <<"Course Name is " <<out <<"Instructor is " <<out <<"Semester/Yr. is " <<return out;
}

const Course &Course::operator=(const Course &right)
{
delete CourseName, instructor, semesterYr;
CourseName = new char[strlen(right.CourseName) + 1];
strcpy(CourseName,right.CourseName);

instructor = new char[strlen(right.instructor) + 1];
strcpy(instructor,right.instructor);

semesterYr = new char[strlen(right.semesterYr) + 1];
strcpy(semesterYr,right.semesterYr);
return *this;
}


void main()
{
Course U("CETH 2261","Jeff","Spring");
cout<}

OK NOW HERE'S MY ISSUES:
The program complies and links fine. However, when I run the app it gives
me a "Debug Assertion Failed" error. Why is that and how do I fix?

Thanks in advance,
eejay

[Chris_W1]

Eejay:

Immediately, I don't see what would cause the assertion failure, but there's a few things that could cause some bizarre and dangerous behavior in your project. Problems like these are very common in C++ and some of them are rather difficult to debug.

(1) I assume that you would like the Course class is allocate memory for and maintain the strings CourseName, instructor, and semesterYr. If that's the case, then it isn't enough to simply assign them in your constructor. Instead, you'll have to allocate memory and copy each string. The constructor currently loads pointers to temporary strings that are later freed.

(2) The fact that you've used the protected access type leads me to believe that you intend to later derive classes from Course. If that's the case, then I suggest you make your destructor virtual.

(3) The #include syntax has slightly changed from C to C++. In C++, library files are supposed to be referenced without any ".h". The older C libraries should also be referenced without the ".h", but they also should have a 'c' prepended to their names. For example, "#include " in C should be written as "#include " in C++. Microsoft Visual C++, for example, will sometimes include a different version of the file if you use the wrong syntax. This can cause errors if you are working with namespaces.

(4) In general, you should use brackets with a delete if you used them with a new. So, in your destructor, you should say

delete [] CourseName;

to be sure that the entire buffer gets freed.

(5) You should check in your assignment operator that you're not being assigned to yourself before you delete anything. For example, with your operator as is,

Course U("CETH 2261","Jeff","Spring");
U = U;

is not likely to behave as you intend.

(6) The use of pointers in your class makes things complicated. Sometimes this is unavoidable, but usually it's not. Because you're managing your own memory, you need to write your own constructor, destructor, copy constructor, and assignment operator. Classes like string in C++ give you the benefits of dynamic sizing of strings without having to worry about managing the heap memory yourself. You may want to take a look at string (or CString if you're using MFC).

I hope this helps. If you're running Microsoft Visual C++, you should be able to press the "Retry" button on the assert dialog and find out where this assertion is occurring.

Good Luck!

Chris Wood
Applications Engineer
National Instruments

[eejay]

Chris,

I'm extremely appreciate for you help on this matter. While reading comment number "(6)" an idea came to mind.

In my constructor, I didn't allocate any memory for the pointer data member.
I coded, for example:

CourseName = cn;

When I should've coded:

CourseName = new char[strlen(cn) + 1];
strcpy(CourseName,cn);

By just assigning cn into CourseName and then trying to print the entire string, I was acessing memory that was not there or allocated. I used this same concept for the other two data members and everything came out fine.

Thanks for all you help,
eejay