#include <iostream>

#include <cstring>

using std::strlen, std::strcpy, std::cin, std::cout, std::endl;

// no two MyString objects point to same "str"

// String.str could not be NULL

class MyString

{

private:

char *str;

public:

MyString(const char *s = "") : str(new char[strlen(s)+1]) { strcpy(str, s); }

MyString(const MyString &s) {MyString(s.str);}

~MyString(){delete[] str;}

const char *to_str() { return str; }

MyString &operator=(const char *s)

{

cout << "call &operator=(const char *s)" << endl;

if (s != str)

{

delete[] str;

str = new char[strlen(s) + 1];

strcpy(str, s);

}

return *this;

}

MyString &operator=(const MyString &z1)

{

cout << "call &operator=(const MyString &)" << endl;

return operator=(z1.str);

}

};

void test_my_string()

{

cout << endl

<< "test_my_string" << endl;

MyString z1("world"), z2, z3;

z2 = "hello ";

z3 = z1;

cout << z2.to_str() << z3.to_str() << endl;

}

void test_cstring()

{

cout << endl

<< "test_ctring" << endl;

char *p = new char[3];

p[0] = '0';

cout << "new char[3]" << endl;

p[2] = '\0';

cout << "p[2]=end strlen: " << strlen(p) << endl;

p[1] = '\0';

cout << "p[1]=end strlen: " << strlen(p) << endl;

p[0] = '\0';

cout << "p[0]=end strlen: " << strlen(p) << endl;

delete[] p;

}

int main()

{

test_cstring();

test_my_string();

return 0;

}