#include <iostream>

#include <string.h>

using namespace std;

class String

{

private:

    int size;

    char *ptr;

public:

    String():size(0),ptr(new char('\0'))

    { cout << "default\n"; }

    String(const String &s):size(s.size)

    {

        cout << "1 param constructor\n";

        ptr = new char[size + 1];

        strcpy(ptr,s.ptr);

    }

    //my code

    String(char *s)

    {

        cout << "2 param constructor\n";

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

        strcpy(ptr,s);

    }    

    ~String()

    {

        delete []ptr;

    }

    friend ostream& operator<<(ostream &,const String & );

    String& operator=(const String &s);

};

//c++ primer第四版中文，435页

//14.2.1 输出操作符的重载：为了与io标准库一直，操作符应接受ostream&作为第一个参数，对类类型const对象的引用作为第2个参数，并返回对ostream形参的引用。

/*friend*/ ostream& operator<<(ostream & os,const String &s)  //这里的friend去掉了！就像类内的static在外面定义时要去掉一样。

                                                          //不去掉的话会报错 error: ‘friend’ used outside of class

{

    return (os << s.ptr);

}

String& String::operator=(const String &s)

{

    cout << "operator=\n";

    if(this != &s)

    {

        delete []ptr;

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

        strcpy(ptr,s.ptr);

    }

    return *this;

}

int main()

{

    String s1 = "hello world";

    String s2 = s1;

    s2 = s1;

    cout << s1 <<endl;

    cout << s2 <<endl;

    return 0;

}

/work/ctest/public_private$ ./1
2 param constructor
1 param constructor
operator=
hello world
hello world

#include <iostream>

#include <string.h>

using namespace std;

class String

{

private:

	int size;

	char *ptr;

public:

	String():size(0),ptr(new char('\0'))

	{ cout << "default\n"; }

	String(const String &s):size(s.size)

	{

		cout << "1 param constructor\n";

		ptr = new char[size + 1];

		strcpy(ptr,s.ptr);

	}

	~String()

	{

		delete []ptr;

	}

	friend ostream& operator<<(ostream &,const String & );

	String& operator=(const char *s);

};

ostream& operator << (ostream & os,const String &s)

{

	return (os << s.ptr);

}

String& String::operator=(const char *s)

{

	cout << "operator=\n";

	//if(this != &s)//这一行代码要注释掉，不然会 error: comparison between distinct pointer types ‘String*’ and ‘const char**’ lacks a cast

	{

		delete []ptr;

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

		strcpy(ptr,s);

	}

	return *this;

}

int main()

{

	String s1 ;

	s1 = "Hello World";

	cout << s1 <<endl;

	return 0;

}