C++ 串代码

字符串类代码，见下

#include
#include
using namespace std;

class String{
private:
	char *str;
	size_t length;
public:
	String();
	String(const char *s);
	String(const String &s);
	~String();
	size_t getLength() const;
	char operator[] (size_t index) const;
	String& operator=(const String& s);
	bool operator ==(const String &s) const;
	bool operator != (const String &s) const;
	String copy() const;
	String operator+(const String &s) const;
	friend ostream& operator<<(ostream &out, const String &s);
};

String::String(){
	length = 0;
	str = new char[1];
	str[0] = '\0';
}

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

String::String(const String &s){
	length = s.length;
	str = new char[length + 1];
	strcpy(str, s.str);
}
String::~String(){
	delete [] str;
}

size_t String::getLength() const{
	return length;
}

char String::operator[](size_t index) const{
	return str[index];
}

String& String::operator=(const String& s){
	if(this != &s){
		delete[] str;
		length = s.length;
		str = new char[length + 1];
		strcpy(str, s.str);
	}
	return *this;
	
}

bool String::operator==(const String& s) const{
	return strcmp(str, s.str)==0;
}

bool String::operator!=(const String& s) const{
	return strcmp(str, s.str)!=0;
}

String String::copy() const{
	String s = *this;
	return s;
}

String String::operator+(const String& s) const{
	String result;
	result.length = length + s.length;
	result.str = new char[result.length + 1];
	strcpy(result.str, str);
	strcat(result.str, s.str);
	return result;	
}

ostream& operator<<(ostream &out, const String &s){
	out << s.str;
	return out;
}

int main(){
	String s("12345d");
	cout << s << endl;
	cout << s + "445" << endl;
	cout << s[5] << endl;
	cout << (s == "12345d") << endl;
	cout << (s != "12345d") << endl;
	s = s + "asd";
	cout << s << endl;
	String a, b, c;
	a = b = c = s;
	cout << s << endl;
	cout << a << b << c << endl;
	String x = s.copy();
	cout << x << endl;
}