C++练习 | 运算符重载练习(字符串相关)

#include <iostream>
#include <cmath>
#include <cstring>
#include <string>
#include <iomanip>
using namespace std;
class String
{
private:
    char *s;
public:
    String()
    {
        s=new char[];
    }
    String(const char *t)
    {
        s=new char[];
        strcpy(s,t);
    }
    String(const String &t)
    {
        s=new char[];
        strcpy(s,t.s);
    }
    ~String()
    {
        delete []s;
    }
    String & operator=(const char *t)
    {
        strcpy(this->s,t);
        return *this;
    }
    String & operator=(const String &t)
    {
        this->s=t.s;
        return *this;
    }
    String operator+(const char *t)
    {
        char *t1=nullptr;
        strcpy(t1,this->s);
        strcat(t1,t);
        return t1;
    }
    String operator+(const String &t)
    {
        char *t1 = nullptr;
        strcpy(t1,this->s);
        strcat(t1,t.s);
        return t1;
    }
    String & operator+=(const char *t)
    {
        strcat(this->s,t);
        return *this;
    }
    String & operator+=(const String &t)
    {
        strcat(this->s,t.s);
        return *this;
    }
    friend istream & operator>>(istream & is, String &t1)
    {
        is>>t1.s;
        return is;
    }
    friend ostream & operator<<(ostream & os, String &t2)
    {
        os<<t2.s;
        return os;
    }
    friend bool operator==(const String &t1, const char *t2)
    {
        if(strcmp(t1.s,t2))
            return ;
        else
            return ;
    }
    friend bool operator==(const String &t1, const String &t2)
    {
        if(strcmp(t1.s,t2.s))
            return ;
        else
            return ;
    }
    friend bool operator!=(const String &t1, const char *t2)
    {
        return strcmp(t1.s,t2);
    }
    friend bool operator!=(const String &t1, const String &t2)
    {
        return strcmp(t1.s,t2.s);
    }
};
int main()
{
    String s;
    s += "hello";
    cout<<s<<endl;
    String s1("String1");
    String s2("copy of ");
    s2 += "String1";
    cout << s1 << "\n" << s2 << endl;
    String s3;
    cin >> s3;
    cout << s3 << endl;
    String s4("String4"), s5(s4);
    cout << (s5 == s4) << endl;
    cout << (s5 != s4) << endl;
    String s6("End of "), s7("my string.");
    s6 += s7;
    cout << s6 << endl;
    return ;
}