0xC0000005: Access violation reading location 0x00000014.

[PKJatt]

This is a parchment of my code which is faulty. In this case I am trying to manipulate multiple linked lists. when I add a new Animal to the list, it gives an error "0xC0000005: Access violation reading location 0x00000014."
It points to the return statement of the following method.

int compare(const _Myt& _Right) const _NOEXCEPT
{ // compare [0, _Mysize) with _Right
return (compare(0, this->_Mysize, _Right._Myptr(), _Right.size()));
}

#include<iostream>
#include<conio.h>
#include<string>
using namespace std;

struct Animal
{
	string name;
	int animal_rarity;
	Animal *a_next;
	Animal()
	{
		animal_rarity = -1;
	}
	void set_values(string str, int num)
	{
		name = str;
		animal_rarity = num;
	}
};

struct Region_Node
{
	string name;
	Region_Node *next;
	int region_rarity;
	Animal *a_head;
	Region_Node()
	{
		a_head = NULL;
		region_rarity = -1;
	}
	void set_values(string a)
	{
		name = a;
	}
	void Add_Animal(Animal* abc)
	{
		Animal  *ptr;
		if(!a_head)
		{
			a_head = abc;
		}
		else
		{
			ptr = a_head;
			while(ptr)
			{
				ptr = ptr->a_next;
			}
			ptr->a_next = abc;
		}
		cout << "\n\n\t\tAnimal Added Successfully. " << endl;
		return;
	}
	bool update_animal_rarity(string str,int a)
	{
		Animal *ptr;
		ptr = a_head;
		if(ptr && ptr->name == str)
		{
			ptr->animal_rarity = a;
			return true;
		}
		else 
		{
			ptr = ptr->a_next;
			while(ptr->a_next && ptr->name != str)
			{
				ptr = ptr->a_next;
			}
			if(ptr->name == str)
			{
				ptr->animal_rarity = a;
				return true;
			}
			return false;
		}
	}
	void animal_list(string str)
	{
		Animal *ptr;
		ptr = a_head;
		if(ptr && ptr->animal_rarity > 0 && ptr->name != "\0")
		{
			cout << "\n\t\tName of Region : " << str << endl;
			cout << "\n\t\tAnimal Name : " << ptr->name <<endl;
			ptr = ptr->a_next;
			while(ptr && ptr->animal_rarity >0 && ptr->name != "\0")
			{
				cout << "\n\t\tAnimal Name : " << ptr->name <<endl;
				ptr = ptr->a_next;
			}
		}
	}
	void search_by_name(string r_name, string str)
	{
		Animal *ptr;
		ptr = a_head;
		if(!ptr)
		{
			return;
		}
		else
		{
			if(ptr->name == str)
			{
				cout << "\tRegion : " << r_name << " \t\tAnimal : " << ptr->name <<endl;
				return;
			}
			else 
			{
				ptr = ptr->a_next;
				while(ptr->a_next && ptr->name != str)
				{
					ptr = ptr->a_next;
				}
				if(ptr->name == str)
				{
					cout << "\tRegion : " << r_name << " \t\tAnimal : " << ptr->name <<endl;
					return;
				}
			}
		}
	}
	void search_by_rarity(string r_name, int b)
	{
		Animal *ptr;
		ptr = a_head;
		if(!ptr)
		{
			return;
		}
		else
		{
			if(ptr->animal_rarity == b)
			{
				cout << "\tRegion : " << r_name << " \t\tAnimal : " << ptr->name <<endl;
				return;
			}
			else 
			{
				ptr = ptr->a_next;
				while(ptr->a_next && ptr->animal_rarity != b)
				{
					ptr = ptr->a_next;
				}
				if(ptr->animal_rarity == b)
				{
					cout << "\tRegion : " << r_name << " \t\tAnimal : " << ptr->name <<endl;
					return;
				}
			}
		}
	}
	bool check_animal_name(string a)
	{
		Animal *ptr;
		ptr = a_head;
		if(!ptr)
		{
			return true;
		}
		else
		{
			while(ptr && ptr->name != a)
			{
				ptr = ptr->a_next;
			}
			if(ptr->name == a)
			{
				return false;
			}
			return true;
		}
	}
	~Region_Node()
	{
		Animal *ptr;
		ptr = a_head;
		while(ptr)
		{
			a_head = ptr->a_next;
			delete ptr;
			ptr = a_head;
		}
	}
};
class Region
{
	Region_Node *head;
public:
	Region()
	{
		head = NULL;
	}
	string get_region_name()
	{
		string str;
		fflush(stdin);
		cout << "\n\n\t\tEnter the Name of the Region : ";
		fflush(stdin);
		getline(cin,str);
		return str;
	}
	void Add_Region()
	{
		Region_Node *newNode , *ptr;
		newNode = new Region_Node;
		newNode->set_values(this->get_region_name());
		newNode->next = NULL;
		if(!head)
		{
			head = newNode;
		}
		else
		{
			ptr = head;
			while(ptr->next)
			{
				ptr = ptr->next;
			}
			ptr->next = newNode;
		}
		cout << "\n\n\t\tRegion Added Successfully ." << endl;
		return;
	}
	string get_animal_name()
	{
		string str;
		fflush(stdin);
		cout << "\n\n\t\tEnter the Name of the Animal : ";
		fflush(stdin);
		getline(cin,str);
		return str;
	}
	int get_animal_rarity()
	{
		int num;
		cout << "\n\n\t\tEnter the Rarity of the Animal : ";
		cin >> num;
		return num;
	}
	Animal* get_Animal()
	{
		Animal *newAnimal;
		newAnimal = new Animal;
		newAnimal->set_values(this->get_animal_name(),get_animal_rarity());
		newAnimal->a_next = NULL;
		return newAnimal;
	}
	void Add_Animal()
	{
		Region_Node *ptr;
		Animal *newAnimal = this->get_Animal();
		ptr = head;
		string name = this->get_region_name();
		if(head)
		{
			if(ptr->region_rarity == -1 || ptr->name == name)
			{
				ptr->Add_Animal(newAnimal);
				this->update_region_rarity(ptr->name);
			}
			else
			{
				ptr = ptr->next;
position:
			{
				while(ptr->next && ptr->region_rarity != -1 && ptr->name != name)
				 {
					ptr = ptr->next;
				 }
				if(ptr->region_rarity == -1 || ptr->name == name)
				 {
					ptr->Add_Animal(newAnimal);
					this->update_region_rarity(ptr->name);
				 }
			}
				if(ptr->next)
				{
					ptr = ptr->next;
					goto position;
				}
				else if(!ptr->next && ptr->next->region_rarity == -1 )
				{
					ptr->next->Add_Animal(newAnimal);
				}
			}
		}

	}
	void update_region_rarity(string str)
	{
		Region_Node *ptr;
		ptr = head;
		if(ptr && ptr->name == str)
		{
			ptr->region_rarity = 10;
			return;
		}
		else 
		{
			while(ptr->next && ptr->name != str)
			{
				ptr = ptr->next;
			}
			if(ptr->name == str)
			{
				ptr->region_rarity = 10;
				return;
			}
		}
	}
	void update_animal_rarity(string str,string str1,int a)
	{
		Region_Node *ptr;
		ptr = head;
		if(ptr && ptr->name == str)
		{
			if(ptr->update_animal_rarity(str1,a))
			{
				cout << "\n\t\tRarity Found And Updated. " << endl;
				this->update_region_rarity(ptr->name);
				return;
			}
		}
		else 
		{
			while(ptr->next && ptr->name != str)
			{
				ptr = ptr->next;
			}
			if(ptr->name == str)
			{
				if(ptr->update_animal_rarity(str1,a))
			    {
				   cout << "\n\t\tRarity Found And Updated. " << endl;
				   this->update_region_rarity(ptr->name);
				   return;
			    }	
				else
			    {
				   cout << "\n\t\tRarity Not Found " << endl;
				   return;
			    }
			}
			return;
		}
	}
	void region_list()
	{
		Region_Node *ptr;
		ptr = head;
		if(head && ptr->name != "\0")
		{
			cout <<  "\n\n\tName of Region : " << ptr->name << endl;
			ptr = ptr->next;
			while(ptr && ptr->name != "\0")
			{
				cout <<  "\n\n\tName of Region : " << ptr->name << endl;
				ptr = ptr->next;
			}
		}
		else 
		{
			cout << "\n\n\t\tRegion List is empty. "<<endl;
			return;
		}
	}
	void animal_list()
	{
		Region_Node *ptr;
		ptr = head;
		if(head)
		{
			ptr->animal_list(ptr->name);
			ptr = ptr->next;
			while(ptr)
			{
				ptr->animal_list(ptr->name);
				ptr = ptr->next;
			}
		}
	}
	void name_search_list(string name)
	{
		Region_Node *ptr;
		ptr = head;
		if(!head)
		{
			cout << "\n\t\tRegion List is Empty. " << endl;
			return;
		}
		else
		{
			while(ptr)
			{
				ptr->search_by_name(ptr->name,name);
				ptr = ptr->next;
			}
		}
	}
	void rarity_search_list(int a)
	{
		Region_Node *ptr;
		ptr = head;
		if(!head)
		{
			cout << "\n\t\tRegion List is Empty. " << endl;
			return;
		}
		else
		{
			while(ptr)
			{
				ptr->search_by_rarity(ptr->name,a);
				ptr = ptr->next;
			}
		}
	}
	~Region()
	{
		Region_Node *ptr;
		ptr = head;
		while(ptr)
		{
			head = ptr->next;
			delete ptr;
			ptr = head;
		}
	}
};

I need urgent help with this. Help would be much appreciated Thank you !

[Cody0023]

1. A debugger will find the problem quickly.
2. Access violation means you are trying to access a variable that has not been allocated.

[cire]

I'm not sure where you're "adding" an animal that is causing this error, as the indicated code is not present in what you posted. Adding an animal through Region::Add_Animal doesn't appear to do anything but leak memory.

If you're looking at a stack trace, you need to follow the trace down until you reach your own code. If you're not looking at a stack trace, you should be.

[PKJatt]

>	Assignment _1.exe!std::basic_string<char,std::char_traits<char>,std::allocator<char> >::compare(const std::basic_string<char,std::char_traits<char>,std::allocator<char> > & _Right) Line 2117	C++

The Call Stack of my code prints this when the exception occurs, by the looks of it , It seems that there is a problem with the "string" allocation, but i don't know how to get rid of this error.

[cire]

If you're looking at a stack trace, you need to follow the trace down until you reach your own code.

For instance, I wouldn't be surprised to learn it originated on line 304 of the code you posted in the OP. Can you see why?

[PKJatt]

Yes, I get it now. Thank you for all your help "cire". Really appreciate it.