C++改造以下函数以友元函数输出

Question

以友元函数的方式重载流插入运算符“<<“:实现字符串的输出

#include <iostream>
using namespace std;
const int maxsize = 256;
class mystring
{
    char str[maxsize];
    int len;
public:
    mystring()
    {
        len = 0;
        str[0] = '\0';
        cout << "缺省构造函数" << endl;
    }
    mystring(char* s)
    {
        int i = 0;
        for (i = 0; s[i] != '\0'; i++)
        {
            str[i] = s[i];
        }
        len = i;
        cout << "构造函数（用C风格字符串初始化）" << endl;
    }
    mystring(mystring& ms)
    {
        len = ms.len;
        for (int i = 0; i < len; i++)
        {
            str[i] = ms.str[i];
        }
        cout << "拷贝构造函数" << endl;
    }
    ~mystring()
    {
        cout << "析构函数" << endl;
    }
    void show()
    {
        for (int i = 0; i < len; i++)
        {
            cout << str[i];
        }
        cout << '\n';
    }
};
int main()
{
    char str[21] = "Hello";
    mystring A(str);
    mystring B ="C++";
    mystring C;
    C = A;
    cout << C;
    C = A + B;
    cout << C;
    return 0;
}

Answer 1

mystring B ="C++";这么写不对啊。代码中有一些错误，也一起改掉了，代码如下：

#include <iostream>
using namespace std;
const int maxsize = 256;
class mystring
{
    char str[maxsize];
    int len;
public:
    mystring()
    {
        len = 0;
        str[0] = '\0';
        cout << "缺省构造函数" << endl;
    }
    mystring(const char* s)
    {
        int i = 0;
        for (i = 0; s[i] != '\0'; i++)
        {
            str[i] = s[i];
        }
        str[i] = 0;
        len = i;
        cout << "构造函数（用C风格字符串初始化）" << endl;
    }
    mystring(mystring& ms)
    {
        len = ms.len;
        for (int i = 0; i < len; i++)
        {
            str[i] = ms.str[i];
        }
        cout << "拷贝构造函数" << endl;
    }
    ~mystring()
    {
        cout << "析构函数" << endl;
    }
    /*void show()
    {
        for (int i = 0; i < len; i++)
        {
            cout << str[i];
        }
        cout << '\n';
    }*/

    friend ostream& operator << (ostream& os,mystring & s);
    friend mystring operator +(mystring& s1, mystring& s2);
    
    
    
};

ostream& operator << (ostream& os, mystring& s)
{
    int i = 0;
    for (; i < s.len && s.str[i] != '\0'; i++)
        cout << (char)s.str[i];
    return os;
}
mystring operator +(mystring& s1, mystring& s2)
{
    mystring s3;
    int i = 0;
    int k = 0;
    while (s1.str[i])
    {
        s3.str[k] = s1.str[i];
        i++;
        k++;
    }
    i = 0;
    while (s2.str[i])
    {
        s3.str[k] = s2.str[i];
        i++;
        k++;
    }
    s3.str[k] = 0;
    s3.len = k;
    return s3;
}

int main()
{
    char str[21] = "Hello";
    mystring A(str);
    mystring B("C++");
    mystring C;
    C = A;
    cout << C;
    C = A + B;
    cout << C;
    return 0;
}