Question

I am new to C++. I am getting HEAP CORRUPTION ERROR. Any help will be highly appreciated. Below is my code

class CEntity  
{  
//some member variables  
CEntity(string section1,string section2);  
CEntity();  
virtual ~CEntity();  
//pure virtual function ..  
virtual CEntity* create()const = 0;  
};  

I derive CLine from CEntity as below

class CLine:public CEntity  
{  
// Again some variables ...  
// Constructor and destructor  
CLine(string section1,string section2);  
CLine();  
~CLine();  
CLine* Create() const;  
}  

// CLine Implementation  
CLine::CLine(string section1,string section2) : CEntity(section1,section2){};  
CLine::CLine();  
CLine* CLine::create() const {return new CLine();}  

I have another class CReader which uses CLine object and populates it in a multimap as below

class CReader  
{  
public:  
CReader();  
~CReader();  
multimap<int,CEntity*>m_data_vs_entity;  
};  

//CReader Implementation  
CReader::CReader()  
{  
  m_data_vs_entity.clear();  
};  

CReader::~CReader()  
{  
  multimap<int,CEntity*>::iterator iter;  
  for(iter = m_data_vs_entity.begin();iter!=m_data_vs_entity.end();iter++)  
  {  
    CEntity* current_entity = iter->second;  
    if(current_entity)  
      delete current_entity;  
  }  
  m_data_vs_entity.clear();  
}  

I am reading the data from a file and then populating the CLine Class.The map gets populated in a function of CReader class. Since CEntity has a virtual destructor, I hope the piece of code in CReader’s destructor should work. In fact, it does work for small files but I get HEAP CORRUPTION ERROR while working with bigger files. If there is something fundamentally wrong, then, please help me find it, as I have been scratching my head for quit some time now.
Thanks in advance and awaiting reply,
Regards,
Atul

Continued from Y’day :
Further studying this in detail I now have realized that Heap allocation error in my case is because I am allocating something, and then overwriting it with a higher size.
Below is the code where in my data gets populated in the constructor.

CEntity::CEntity(string section1,string section2)
{
    size_t length;
    char buffer[9];
    //Entity Type Number
    length = section1.copy(buffer,8,0);
    buffer[length]='\0';
    m_entity_type = atoi(buffer);

    //Parameter Data Count
    length = section1.copy(buffer,8,8);
    buffer[length]='\0';
    m_param_data_pointer = atoi(buffer);
        //.... like wise ....
}

I am getting the values at a fixed interval of 8 chars and I am adding a ‘\0’ so this, i guess will take care of any garbage value that I encounter.

About
Heap allocation error: after normal block (XXX) at XXX, CRT detected that application wrote to memory after end of Heap buffer. Mostly, Heap allocation errors occur somewhere else than where it crashes. I would appreciate if some one here would help me, how to make use of this normal block and the address.
Thanks,

Answer 1

Finally, after two days of debugging, I was able to fix up the crash. It was due to me copying wrong number of characters from the string.
Lessons learnt :
1. When you encounter memory allocation errors, try to form a simple test case which has minimum entities to reproduce the problem.
2. A sure shot way is a line by line debugging. I agree,it test your patience, but then, there are no short cuts to success
3. And it gives you a chance to do a code review, further enhancing the quality of code that you produce in future

Thank you for all your help and formatting my code 🙂
Regards,
Atul