赋值运算符的重载

“=”重载的概念

#include <bits/stdc++.h>
using namespace std;
class String
{
    private:
        char *str;
    public:
        String(void);
        String(const String &);
        void PrintString(void);
        String& operator=(const char*);
        ~String(void);
};
String::String(void):str(new char[1])
{
    str[0]='\0';
}
String::String(const String &s)
{
    str=new char[strlen(s.str)+1];
    strcpy(str,s.str);
}
String& String::operator=(const char *s)
{
    delete [] str;
    str=new char[strlen(s)+1];
    strcpy(str,s);
    return *this;
}
void String::PrintString(void)
{
    cout<<str<<endl;
}
String::~String(void)
{
    delete [] str;
}
int main(void)
{
    String s;
    s="Hello";
    s.PrintString();//Hello
    //String s2="Hello"; //Error 是赋值而不是初始化
    s="World";
    s.PrintString();//World
    return 0;
}

深拷贝和浅拷贝

考虑语句”String s1=”Hello”;String s2=”World”;s1=s2;”

String& operator=(const String &s)
{
    if(this==&s)
        return *this;//防止有人写s=s这种语句而产生不必要的错误
    delete [] str;
    str=new char[strlen(s.str)+1]；
    strcpy(str,s.str);
    return *this;
}