c++实现 String 类

 实现Stirng类：普通构造、复制构造、赋值函数、重载输出函数 <<（友元） 

#include <iostream>
#include <string.h>
#include <stdlib.h>
using namespace std;

class String 
{
    public:
        String (const char *str=NULL); //普通构造函数
        String (const String &other);  //复制构造函数
        ~String (void); //析构函数
        String &operator=(const String &other); //赋值函数
        friend ostream &operator<<(ostream &output, const String &other); //输出函数
    private:
        char *data; //保存字符串
};

//普通构造函数
String::String(const char *str)
{
    if (str == NULL)
    {
        data = new char[1];
        *data = '';
    }
    else
    {
        int len = strlen(str);
        data = new char[len+1];
        strcpy(data, str);
    }
}

//复制构造函数
String::String(const String &other)
{
    int len = strlen(other.data);
    data = new char[len+1];
    strcpy(data, other.data);
}

//析构函数
String::~String()
{
    delete[] data;
}

//赋值函数
String &String::operator=(const String &other)
{
    if (this == &other)
    {
        return *this;
    }
    delete[] data;

    int len = strlen(other.data);
    data = new char[len+1];
    strcpy(data, other.data);

    return *this;
}

//输出函数
ostream &operator<<(ostream &output, const String &other)
{
    output<<other.data;
    return output;
}

int main()
{
    String s1("hello");
    cout << s1 << endl;
    String s2=s1;
    cout << s2 << endl;
    String s3;
    s3=s1;
    cout << s3 << endl;
}