string类的成员函数

#include <iostream>
using namespace std;

class String
{
public:
	String(const char* str =NULL);
	String(const String &another);
	~String();
	String& operator=(const String &rhs);

	void Print();
protected:
private:
	char* m_data;
};

String::String(const char* str /* =NULL */)
{
	if (str == NULL)
	{
		m_data = new char[1];
		m_data[0] = '\0';
	}
	else
	{
		m_data = new char[strlen(str)+1];
		strcpy(m_data,str);
	}
}

String::String(const String &another)
{
	m_data = new char[strlen(another.m_data)+1];
	strcpy(m_data,another.m_data);
}

String::~String()
{
	delete []m_data;
}

String& String::operator=(const String &rhs)
{
	if (this == &rhs)
		return *this;
	delete []m_data;
	m_data = new char[strlen(rhs.m_data)+1];
	strcpy(m_data,rhs.m_data);
	return *this;
}


void String::Print()
{
	cout<<m_data<<endl;
}

void main()
{
	String a("abcdefg");
	String b(a);
	String c=b;
	a.Print();
	b.Print();
	c.Print();
}