模拟实现string类

#include<iostream>
#include<string.h>
#include<fstream>
using namespace std;
class String
{
private:
char *_s;
public:
String(const char* s = "")                        //构造函数
{
_s = new char[strlen(s) + 1];
strcpy(_s, s);
}
String(const String &p)                                 //拷贝构造函数
{
_s = new char[strlen(p._s) + 1];
strcpy(_s, p._s);
}
~String()                                     //析构函数
{
if (_s)
{
delete[] _s;
_s = NULL;
}
}
String &operator=(const String &p)                             //赋值运算符重载
{
if (this == &p) return *this;
delete _s;
_s = new char[strlen(p._s) + 1];
strcpy(_s, p._s);
return *this;
}
String operator+(const String &p)                                  //+重载
{
String temp;
temp._s = new char[strlen(_s) + strlen(p._s) + 1];
strcpy(temp._s, _s);
strcat(temp._s, p._s);
return temp;
}
friend ostream &operator << (ostream &out, String &p);                  //<<插入运算符重载（友元）
};
ostream &operator << (ostream &out, String &p)
{
out << p._s << endl;
return out;
}
void main()
{
String p1 = "张三 ", p2 = " 李四",p3;
p3 = p1;
String p4(p2);
String p5 = p1 + p2;
cout << "p1 = "<<p1;
cout << "p2 = "<<p2;
cout << "p3 = p1 = "<< p3;
cout << "p4 = p2 = " << p4;
cout << "p5 = p1 + p2 = "<< p5;

}

运行结果：