new [] / delete [] errors, going crazy!

I am writing a program that allows for the creation of a theoretically infinitely large integer. I have created the class MyInt and implemented the storage using DMA.
I have attached the .cpp and .h files. These are not the complete files, there are several other overloads but for simplocity sake I narrowed it down to only those functions involved in the problem.
I have placed many cout statements in here trying to trace the problem. And the problem seems to be in the Grow() function that increases the size of the array. Any help would be greatly appreciated.

Thanks in advance.

Yes in Grow you use delete instead of the proper delete[]

Why struggle with all this memory management yourself? You could use a std::vector<unsigned int> instead.

EDIT: std::vector<unsigned char> would be better to avoid current waste of memory (or change to use binary arithemetic)

It's an assignment. They don't want you using things that might make your life too easy. I still can't use the string class much less vectors. I have tried putting the [] in there and it doesn't work either. I have tried everything I can think of. I have never been so stumped. There error I am getting starts with this, and then the "memory map" which I am not experienced enough to understand.

*** glibc detected *** ./myint: free(): invalid next size (fast): 0x099bc020 ***

It crashes when it tries to use delete. From the research I have done this error is often times caused by trying to delete an object/variable that was not created using new. Not sure I can see how that is the case here. It seems like amybe I am doing something wrong in line 178 where this is:

unsigned int *newArray = new unsigned int[maxSize];

Thanks again.

I would guess that you write out of bounds in either MyInt(int n) or the + operator. Have you runned the code in a debugger?

EDIT: Have you tried using numbers <= 99999? For numbers > 99999 I guess this was supposed to kick in but it's not

Code:

---

int i = 0;
while(i != 0) // Guess you meant to have n here?
{
    intArray[i] = n % 10;
    n = n/10;
    currentSize++;

    if(currentSize == maxSize)
      Grow();
    i++;
}

---

Quote:

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Originally Posted by weaverx9x9

It's an assignment. They don't want you using things that might make your life too easy.

---

Using container and string classes make things easier in terms of having working components that you can use to build the larger application. However, you still have to write the program using these components, so that part is still not "easy", but at least your thinking is now geared towards solving the actual problem that needs to be solved.

Having said that, C++ beginner courses that still teach C++ as if it's 1990 and not 2010 should be abolished (if I had my way). It's the year 2010, and string classes, vectors, etc. have been standardized in C++ since 1998. I wish these courses were honest, and say you are learning 'C' and not C++.

Regards,

Paul McKenzie

Another issue is your assignment operator:

Code:

---

if(this != &n)
 {
        delete [] intArray;
        intArray = new unsigned int[n.currentSize];

---

What happens if new[] throws an exception? You've messed up your object by deleting your data.

Code:

---

if(this != &n)
 {
      unsigned int *temp = new unsigned int[n.currentSize];
      //...
      // copy data into temp
      //
      //
    delete [] intArray;
    intArray = temp;
    //
  }

---

Now the memory is allocated before anything is done. If new[] throws an exception, then your original intArray is still intact.

Regards,

Paul McKenzie

Yeah your're right let me try that. I did mean n, not i.

Thanks Paul, actually most of that code block came from an example program from my proffessor. I will take a look at it again and see if I can find something. I had to take a break starting to see cross eyed and want to break stuff, just kidding. Thanks again, I will post what I find when I look at it.

Quote:

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Originally Posted by weaverx9x9

Thanks Paul, actually most of that code block came from an example program from my proffessor.

---

If it came from your professor, then it's quite revealing that he/she didn't see this issue, as anyone who is responsible for teaching a complex language such as C++ should/would have corrected it.

More than likely, C++ is not this teacher's main programming language, which can be an issue when it comes to teaching C++ (as opposed to teaching other computer languages).

Regards,

Paul McKenzie

Actually c++ is his main course. I took him for intro to c++ and am currently taking oop with him. He has a Ph.d in something I'm guessing computer science.

Quote:

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Originally Posted by weaverx9x9

He has a Ph.d in something I'm guessing computer science.

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You may be surprised to learn that having a qualification in computer science has no bearing on your ability to program (or ever have programmed) in any computer language. :eek:

Quote:

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Originally Posted by weaverx9x9

It's an assignment. They don't want you using things that might make your life too easy. I still can't use the string class much less vectors.

---

When you think you've got the hang of dynamic memory allocation, then maybe you could write you own simple string and vector classes and use them in future assignments that ban the STL. They can't complain about that!

I have actually considered that. I wasn't sure which would be more work though, writting the vector and string classes or just using the libraries permitted. Next semester I'm taking data structures and algorithms. Apparently in that class they introduce the STL so I'm guessing at that point we will be able to use more of the libraries.

In the prereq course intro to c++ we weren't even alowwed to use iomanip or cctype. We had to use ios:: to format output. I understand why they did it this way it's kind of like in math they didn't want you to use a calculator until you got to a certain level. It's just frustrating to know there is a tool that could make what I am trying to do allot easier.

I was actually dreaming about this program last night. I think I got something, but I need to take a look at it first.

Quote:

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Originally Posted by weaverx9x9

I understand why they did it this way it's kind of like in math they didn't want you to use a calculator until you got to a certain level.

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That would be a defensible argument (though I still won't agree with it) iff you were taught to write completely safe programs. But as Paul has pointed out, the code provided by your professor is not safe. Hence, you are simply being taught bad programming practices, rather than the basics.

Yeah that's true D_Drmmr.

I changed the overload of the assignment operator to reflect what Paul McKenzie suggested. I am still getting the same error though. I am going to stop by one of my teching assistants offices today at school. But I have to say, I don't have allot of faith in those guys.

const MyInt MyInt::operator= (const MyInt& n)
{
if(this != &n)
{
// Create an array to copy data to before deleting intArray
// in case an exception is thrown.
unsigned int *temp = new unsigned int[n.currentSize];
for(int i = 0; i < n.currentSize; i++)
{
temp[i] = n.intArray[i];
}

// Delete the old array.
delete [] intArray;
// Assign the new array pointer to original.
intArray = temp;
// Assign the size information.
currentSize = n.currentSize;
maxSize = n.maxSize;
}
return *this;
}

Sorry about the formatting on that code block, I am not very experienced with that. Obviously the overload is not the :operator= overload. I feel pretty certain the problem is in the Grow() function. But it may be caused by the creation of the intArray else where.

Quote:

---

Originally Posted by weaverx9x9

Sorry about the formatting on that code block, I am not very experienced with that. Obviously the overload is not the :operator= overload. I feel pretty certain the problem is in the Grow() function. But it may be caused by the creation of the intArray else where.

---

To check if your object is copied correctly, you can write a simple test program. Something like this

Code:

---

// include MyClass

int main()
{
    MyClass a; // default c'tor
    MyClass b(...); // parameterized c'tor
    MyClass c = b; // copy c'tor
    a = c; // assignment operator

    // possibly do some tests
}

---

Check not only that the objects are proper copies, but also that all memory is freed an no double deletes are performed.

I have a driver program, and I can successfully use the assignment operator. It is at the addition that I run into problems. But after putting several cout statements in my program I have traced the problem to the Grow() function. It seems to be a problem with the line where I have

delete [] intArray

in the Grow() function on line 193 of the files I attached.

If you have operator+= tested and working, and if you have the cctor and operator= tested and working, then there is absolutely no reason why operator+ would not work. So focus on the components first-----is the problem in the copying, or in the += operation?

I haven't overloaded the += operator. And I have even been able to get it to add two numbers. The problem is when the array reaches the upper bound and I call the Grow() function to increase the size of the array it is giving me a bad allocation error. It's not just giving me a segmentation fault it's scrolling a whole bunch of stuff on the screen, it says memory map, and shows stack and heap and memory addresses. I don't know how to use that stuff to help me, it might as well be chinese. It may be that there is a problem in the operator+ function, but it crashes in the Grow() function. I read something about debugging though that said that instead of using printf or cout statements that you should use stderr since it isn't buffered. But I can't remember how to do that. Is it

stderr::cout <<

or is it just stderr <<

?

cerr <<

Quote:

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Originally Posted by weaverx9x9

I haven't overloaded the += operator.

---

That is what you should have done first. Maybe you should forget operator + for now, and concentrate on operator +=. Once you get operator += working, operator + will literally take 15 seconds to write, as operator + will just use += to do the work.

Quote:

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And I have even been able to get it to add two numbers. The problem is when the array reaches the upper bound and I call the Grow() function to increase the size of the array it is giving me a bad allocation error.

---

This goes to my point I made before. You have an assignment that is supposed to add big numbers -- when are you going to actually add the numbers? You haven't even gotten that started. If you were allowed to use containers, all of these allocation issues become moot, and you can then concentrate on the real goal of the assignment, and that is a class that adds big numbers.

This IMO is how a beginner C++ program should be taught, and that is for the student to concentrate on the goal and use standard containers, algorithms, classes, etc. to reach that goal. Instead of putting together the jigsaw puzzle, you've been told to get cardboard, glue, a pretty picture, a knife, and create the jigsaw puzzle yourself.

I can tell you this -- Java students would not have to go through this as you have -- they are required to use the components and not code their own containers and strings.

Quote:

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It's not just giving me a segmentation fault it's scrolling a whole bunch of stuff on the screen, it says memory map, and shows stack and heap and memory addresses. I don't know how to use that stuff to help me, it might as well be chinese. It may be that there is a problem in the operator+ function, but it crashes in the Grow() function.

---

Let's look at Grow:

Code:

---

void MyInt::Grow()
{
    maxSize = currentSize + 5;
    unsigned int *newArray = new unsigned int[maxSize];
   
    for(int i = 0; i < currentSize; i++)
        newArray[i] = intArray[i];
   
    // delete  intArray;  // wrong form of delete!
    delete [] intArray;
   
    intArray = newArray;
   
  //    newArray = NULL;  // no need for this line.
 
  // Now where do you reset currentSize to maxSize?
  // Isn't that missing?
}

---

1) You are using the wrong form of delete,

2) You do not set currentSize to the maxSize after all of this work. So what is probably happening is that Grow() is not growing anything, since you use the stale value of currentSize every time. If you're setting currentSize somewhere else, don't. Do it right there in Grow(), otherwise you're jumping around all over the place setting currentSize, when the logical place to set it once and for all is before Grow() returns.

In addition, you have a superfluous line that sets newArray to NULL.

Regards,

Paul McKenzie

Quote:

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Originally Posted by JohnW@Wessex

When you think you've got the hang of dynamic memory allocation, then maybe you could write you own simple string and vector classes and use them in future assignments that ban the STL. They can't complain about that!

---

Yes indeed ! :)

I got it working! Haven't added all the operator overloads yet. It would seem that the problem was in the operator+ function. Still not sure what i did wrong exactly. I know though that I was somehow writing way out of bounds when creating a new array in the Grow() function. That's why I thought the problem was in the Grow() function because that's where it crashed. It was trying to dynamically create an array of like 3 billion ints or maybe it was more can't remember but it was a really long number.

I appreciate all of the help. This is the first forum that I have ever been a member of. I was surprised to see how helpful people were.

Quote:

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Originally Posted by weaverx9x9

I got it working! Haven't added all the operator overloads yet. It would seem that the problem was in the operator+ function. Still not sure what i did wrong exactly.

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Is the header still the same, or did you just change the cpp file? I will take a look at your new code and comment if I see anything else glaringly wrong. I have a habit of destroying all hopes of new programmers by breaking their code with a very simple main() program, so just be aware. :)

Quote:

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I appreciate all of the help. This is the first forum that I have ever been a member of. I was surprised to see how helpful people were.

---

As long as you ask questions in detail, with a description of what problems you're having, then you will get all sorts of help here. The only thing you won't get is anyone to do the work for you (and I believe you knew that already).

Regards,

Paul McKenzie

Here are some things with the new code you should address:

Code:

---

MyInt::MyInt(const char* n)

---

Since "n" doesn't have it's contents it's pointing to change, this should be const char*.

I still don't understand why you do not update the size member in the Grow() function. Maybe that's where you're getting tied up in knots. I would expect Grow() to actually dynamically allocate memory, and at the same time, update "size" so that it now has the current size that is allocated.

What if you called Grow() twice in succession? You see that your "size" member variable never changes, and this to me is not correct in a logical sense. That's why you should change "size" in the function where it counts, and that is in Grow(). Right now, you're changing size all over the place except in the place where it makes sense.

Code:

---

size = 1;
Grow();
Grow();
Grow();

---

You will see nothing grows, even though I called it three times!

Regards,

Paul McKenzie

That's a good idea on the constructor with the char* n parameter. The grow() function is basically creating a dynamically allocated array that is 5 slots (indices not sure about the term here) larger than size. Size is the current length of the array and Max is the upper limit. Basically just so we're not dynamically creating and destroying memory and copy data every time the size is increased.
I did make some modifications to the header file, I will post it tomorrow when I get up.
I welcome any attempts to "break" my program. And I'm sure it won't be hard. Like math I enjoy programming and am always open to advice to improve my abilities/skills. The program isn't quite complete yet but what is done works (gives the proper result given the inputs I've tested so far).

Weaver

Well, I fixed the addition part, and then added the multiplication. However, once I implemented the multiplication operator overload I started getting the same error. I have been getting two memory errors. One is a segmentation fault and the other is: " *** glibc detected *** ./myint: malloc(): memory corruption (fast) : 0x08e7c110 *** "

The assignment was due at that point so I just turned it in as it was. It compiles, it just crashes. It would seem that the error is taking place when multiplying an int times a myint object. The multiplication works on two myint objects. This leads me to believe that the problem is an object conversion issue. But I have the default constructor set up to accept ints. So not sure. Since the program was due this is no longer for credit but I am in school to learn this stuff so I would like to understand what I did wrong if I can. I am going to meet with my professor next week if I can (he's always pretty busy), his teaching assistants weren't allot of help. I am attaching the .cpp, .h, driver and the make file in a tar file.

Happy veterans day to everyone.

Weaver