C++实现String

# include <iostream>
# include <memory>
# include <cstring>
using namespace std;
class MyString {
private:
    char *m_data;
public:
    MyString();
    MyString(const char* ptr);
    MyString(const MyString& rhs);
    ~MyString();
    MyString& operator=(const MyString& rhs);
    MyString operator+(const MyString& rhs);
    char operator[](const unsigned int index);
    bool operator==(const MyString& rhs);
    friend ostream& operator<<(ostream& output, const MyString &rhs);
};
//默认的构造函数
MyString::MyString() {
    m_data = new char[];
    *m_data = '\0';
}
//使用const char* 来初始化
 MyString::MyString(const char* ptr) {
    if (NULL == ptr) {
        m_data = new char[];
        *m_data = '\0';
    } else {
        int len = strlen(ptr);
        m_data = new char[len + ];
        strcpy(m_data, ptr);
    }
}
//拷贝构造函数
MyString::MyString(const MyString& rhs) {
    int len = strlen(rhs.m_data);
    m_data = new char[len + ];
    strcpy(m_data, rhs.m_data);
}
bool MyString::operator ==(const MyString& rhs) {
    int result = strcmp(m_data, rhs.m_data);
    if ( == result)
        return true;
    else
        return false;
}
//赋值操作符
MyString& MyString::operator =(const MyString& rhs) {
    if (this != &rhs) {
        delete[] m_data;
        m_data = new char[strlen(rhs.m_data) + ];
        strcpy(m_data, rhs.m_data);
    }
    return *this;
}
//重载运算符+
MyString MyString::operator+(const MyString &rhs) {
    MyString newString;
    if (!rhs.m_data)
        newString = *this;
    else if (!m_data)
        newString = rhs;
    else {
        newString.m_data = new char[strlen(m_data) + strlen(rhs.m_data) + ];
        strcpy(newString.m_data, m_data);
        strcat(newString.m_data, rhs.m_data);
    }
    return newString;
}
//重载下标运算符
 char MyString::operator [](const unsigned int index) {
    return m_data[index];
}
//析构函数
MyString::~MyString() {
    delete[] m_data;
}
//重载<<
ostream& operator<<(ostream& output, const MyString &rhs) {
    output << rhs.m_data;
    return output;
}
int main() {
    const char* p = "hello,world";
    MyString s0 = "hello,world";
    MyString s1(p);
    MyString s2 = s1;
    MyString s3;
    s3 = s1;
    MyString s4 = s3 + s1;
    bool flag(s1 == s2);
    cout << s0 << endl;
    cout << s1 << endl;
    cout << s2 << endl;
    cout << s3 << endl;
    cout << flag << endl;
    char result = s3[];
    cout << result << endl;
    cout << s4 << endl;
    return ;
}