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Copy on Write program

zanklob (39)
Hi,
I am trying to make copy on write program, but I get a Segmentation fault after my first result (String kiri has : 1 pointer(s).)

It is mandatory for my program to have a class(StringHolder) that will keep a pointer to a string.
and I am supposed to create my StringHolder objects like this : a("kiri").
If there is a b("kiri"), it has to redirect the pointer to the first string in order to save memory.
I have done it a little differently than I should but I don't get the segmentation fault.

Thanks in advance!!!


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#include <iostream>
#include <cstring>
#include <string>
#include <map>
//changes

//A class that keeps count of how many pointers point to each string
class U_Ptr
{


public:

U_Ptr() {}

/*U_Ptr(std::string* p) : ip(p)
{
	pointer_count[ip] = 1;
}*/

~U_Ptr()
{
//	pointer_count.clear();
}

std::string* AddString(std::string* a_Data)
{
	std::string* m_pStr;
	std::string m_Str;
	std::string m_Data;
	m_Data = *a_Data;
//	Map_Type::iterator iter = pointer_count.find(a_Data); //psakse me vash to periexomeno tou pointer kai oxi ton pointer (isws proswrinh metavlhth gia na krathsei to periexomeno)
	if (pointer_count.empty())
	{
		pointer_count.insert(std::pair<std::string*, int>(a_Data, 1));
		return a_Data;
	}
	else
	{

		for (Map_Type::iterator iter = pointer_count.begin(); iter != pointer_count.end(); ++iter)
		{
			m_Data = *a_Data;
			m_pStr = iter->first;
			m_Str = *m_pStr;
			if (m_Data.compare(m_Str) == 0)
			{
				a_Data = iter->first;
				++iter->second;
			}
			else
				pointer_count.insert(std::pair<std::string*, int>(a_Data, 1));
		}

	}

}

void DeleteString(std::string* a_Data)
{
	Map_Type::iterator iter = pointer_count.find(a_Data);
	if (iter->second == 1)
	{
		pointer_count.erase(iter);
	}
	else
	{
		--iter->second;
	}
}
void PrintString(std::string* a_Data)
{
	Map_Type::iterator iter = pointer_count.find(a_Data);
    std::cout << "String " << *iter->first << " has : " << iter->second << " pointer(s)." << std::endl;
}

private:
friend class StringHolder;
typedef std::map<std::string*, int> Map_Type;
Map_Type pointer_count; //A map that counts how many pointers to each std::string exist

};//class U_Ptr

//A class that keeps a pointer to a std::string object
class StringHolder
{
public:
	StringHolder(std::string* a_Data, U_Ptr& a_ptr)
	{
//		ptr = new U_Ptr(a_Data);//creates a pointer to a U_Ptr object
		m_Data = a_Data;
		m_ptr = &a_ptr;
		m_Data = (*m_ptr).AddString(m_Data);
	}

	void operator+=(std::string rhs)
	{
		std::string temp = (*m_Data);
	    temp.append(rhs);
		(*m_Data) = temp;
		(*m_ptr).AddString(m_Data);
//	    std::cout << *m_Data << std::endl;
	}

	~StringHolder()
	{
		(*m_ptr).DeleteString(m_Data);

	}
	void Print()
	{
		(*m_ptr).PrintString(m_Data);
	}

private:
	U_Ptr* m_ptr;
	std::string* m_Data;

};//class StringHolder


int main()
{
	U_Ptr ptr;

	std::string test = "kiri";
	std::string test2 = "Oleg";
	std::string test3 = "kiri";
	std::string* p_test = &test;
	std::string* p_test2 = &test2;
	std::string* p_test3 = &test3;
	StringHolder a(p_test, ptr);
	a.Print();
	StringHolder b(p_test, ptr);
	b.Print();
	b += "Luc";
	b.Print();
	StringHolder c(p_test2, ptr);
	c.Print();
	StringHolder d(p_test3, ptr);
	d.Print();
	return 0;
}
cire (8284)
Please don't make duplicate threads.

http://www.cplusplus.com/forum/beginner/81321/
zanklob (39)
Yes i am sorry i will delete the second.
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