C++ 字符串重载运算符

#include<iostream.h>
#include<string.h>
//using namespace std;
class Cstring
{
public:
	Cstring()
	{
		p = new char[1];
		*p = '\0';
	}
	Cstring(const char *t);
	Cstring(const Cstring &t);
	~Cstring()
	{
		delete[]p;
	}
	bool operator<(const Cstring &t)const;
	friend bool operator > (const Cstring &str1,const Cstring &str2);
	Cstring& operator=(const Cstring &t);
	Cstring operator+(const Cstring &t)const;
	bool operator==(const Cstring &t)const;
	char& operator[](int index);

	void Show()
	{
		cout<<p<<endl;
	}
private:
	char *p;
};

Cstring::Cstring(const char *t)
{
	if(t == NULL)
		t = "";
	int n = strlen(t);
	p = new char[n+1];
	strcpy(p,t);
}
Cstring::Cstring(const Cstring &t)
{
	p = new char[strlen(t.p)+1];
	strcpy(p,t.p);
}
bool Cstring::operator <(const Cstring &t)const
{
	if(strcmp(p, t.p) < 0)
		return true;
	else return false;
}
bool operator > (const Cstring &str1, const Cstring &str2)
{
	if(strcmp(str1.p, str2.p) > 0)
		return true;
	else return false;
}
bool Cstring::operator ==(const Cstring &t)const
{
	return strcmp(p,t.p) == 0;
}
char& Cstring::operator [](int index)
{
	return p[index];
}
Cstring Cstring::operator +(const Cstring &t)const
{
	char *pt;
	pt = new char[strlen(p)+strlen(t.p)+1];
	strcpy(pt,p);
	strcat(pt,t.p);
	Cstring temp(pt);
	delete[]pt;
	return temp;
}
Cstring& Cstring::operator =(const Cstring &t)
{
	if(this == &t)
		return *this;
	delete[]p;
	p = new char[strlen(t.p)+1];
	strcpy(p,t.p);
	return *this;
}

void main()
{
	Cstring s1("Hello");
	Cstring s2("World");
	Cstring s3;
	s1.Show();
// 	if(s1[0]>='A' &&s1[0]<='Z')
// 		s1[0] = s1[0]+32;
// 	s1.Show();
	cout <<(s1>s2)<<endl;
	cout <<(s1<s2)<<endl;
	s3 = s1;
	s3.Show();
	s3 = s1+s2;
	s3.Show();
}

在VC6.0下如果将头文件改为：

#include<iostream>

#include<string.h>

using namespace std;

就会出现下列错误

error C2248: ‘p‘ : cannot access private member declared in class ‘Cstring‘