Debug assertion failed BLOCK_TYPE_IS_VALID(pHead->nblockuse) from Deconstructor

Question

I am quite lost right now. I made a vector class. Everything works how I would like it to work, until the end. When the destructor is called I get an error message: Debug assertion failed BLOCK_TYPE_IS_VALID(pHead->nblockuse). I've seen quite a few questions like this one on SO, but what I have tried hasn't worked.

part of .h.

private:
    int* _myArray;
    int _size;
    int _capacity;

#include "File.h"

 const string RETURN_CARRIAGE_STR = "\n";
 const string SIZE_STR = "Size ";
 const string CAPACITY_STR = "Capacity ";
 const int INITIAL_CAPACITY = 2;

 int main(void)
{
cout << "\nCreating a vector Sam of size 4.";
MyVector sam( 4 );

cout << "\nPush 12 values into the vector.";
for (int i = 0; i < 12; i++)
    sam.push_back(i);

cout << "\nHere is sam: ";
cout << sam;
cout << "\n---------------\n";

    cout << "\nCreating a vector Joe of size 4.";
MyVector joe( 4 );
cout << "\nPush 6 values into the vector.";
for (int i = 0; i < 6; i++)
    joe.push_back(i * 3);

cout << "\nHere is joe: ";
cout << joe;
cout << "\n---------------\n";

cout << "\nTest the overloaded assignment operator \"joe = sam\": ";
joe = sam;


cout << "\nHere is sam: ";
cout << sam;
cout << "\n---------------\n";

cout << "\nHere is joe: ";
cout << joe;
cout << "\n---------------\n";

// pass a copy of sam by value
PrintV(sam);

cout << endl;
system("PAUSE");
 }

 void PrintV(MyVector v)
 {
cout << "\n--------------------\n";
cout << "Printing a copy of a vector\n";
cout << v;
 }

 // Default Constructor
 MyVector::MyVector()
 {
_myArray = new int[INITIAL_CAPACITY];
_size = 0;
_capacity = INITIAL_CAPACITY;
//cout << "Default Constructor" << endl;
 }

 MyVector::MyVector(int aSize)
 {
_myArray = new int[aSize];
_size = 0;
_capacity = aSize;

//cout << "Parameterized Constructor" << endl;
 }

 MyVector::~MyVector()
 {
if(_myArray != NULL)
{
    delete[] this->_myArray; //  --------------This is where I get an error
    this->_myArray = NULL;
}

//cout << "Destructor" << endl;
 }


 int MyVector::GetSize()
 {
return _size;
//cout << " size";
 }

 int MyVector::GetCapacity()
 {
return _capacity;
//cout << _capacity << " capacity" << endl;
 }

 void MyVector::Clear()
 {
int* resize_arr = new int[INITIAL_CAPACITY];
delete[] _myArray;
_myArray = resize_arr;
_capacity = INITIAL_CAPACITY - 1;
_size = 0;
 }

 void MyVector::push_back(int newValue)
 {
if(_size < _capacity)
{
    _myArray[_size] = newValue;
}
else  {
    int* resize_arr = new int[_capacity*2];
    for(int i = 0; i <= _size; i++)
        resize_arr[i] = _myArray[i];

    resize_arr[_size] = newValue;
    delete[] _myArray;
    _myArray = resize_arr;
    _capacity = _capacity * 2;
}
_size++;
//cout << _size << " size" << endl;
 }

 int MyVector::at(int idx)
 {
return _myArray[idx];
//cout << _myArray[idx] << " value at index" << endl;
 }

 ostream& operator<<(ostream& os, MyVector& vec)
 {
ostringstream convert;
ostringstream convertCap;
convert << vec.GetSize();
string sizeConverted = convert.str();
convertCap << vec.GetCapacity();

string capConverted = convertCap.str();
string firstTemp = "";
firstTemp = SIZE_STR + sizeConverted  + RETURN_CARRIAGE_STR + CAPACITY_STR + capConverted + RETURN_CARRIAGE_STR;

for(int idx = 0; idx < vec.GetSize(); idx++)
{
    string secondTemp = "";
    ostringstream convertSize;
    convertSize << vec.at(idx);
    string vecAtIdx = convertSize.str();
    secondTemp = vecAtIdx + RETURN_CARRIAGE_STR;
    cout << secondTemp;
}

os <<  firstTemp;
return os;
 }

 MyVector& MyVector::operator=(MyVector& setterVect)
 {
delete [] _myArray;

//MyVector* mPtr = new MyVector();

_myArray = setterVect._myArray;
_capacity = setterVect._capacity;
_size = setterVect._size;

return *this;
 }

Answer 1

_myArray = setterVect._myArray;

Your copy assignment operator is broken. After that operator, both instances have the same value for _myArray. So as soon as one is destructed, the other one is left with a pointer to something that no longer exists.

And the moral of the story -- use std::vector.

Answer 2

The error means heap corruption. There are lots of ways to corrupt a heap. Like David explained above, freeing a chunk of memory and then writing to it is one way.

Most heaps store some bytes of bookkeeping information before and after your chunk of memory. If your code misbehaves and changes the heaps data, you get this type of error.