记录一次给QQ好友讲解class的构造拷贝构造 拷贝赋值（浅拷贝、深拷贝赋值）

#include <iostream>
#include <cassert>
#include <cstdlib>

using namespace std;
char* my_strcpy(char* dest, char *src) 
{
    assert(dest != NULL && src != NULL);
    char *ret = dest;
    while ((*dest++ = *src++)!= '\0');
    return ret;
}
int my_len1(const char *mystr) {
    // '/0'
    int len = 0;
    assert(mystr);
    while (*(mystr++) != '\0') 
    {
        len++; 
    }
    return len;
}
int my_len2(const char *mystr) {
    //递归
    assert(mystr);
    //递归结束条件
    if (*mystr == '\0') {
        return 0;
    } else {
        return (1 + my_len2(++mystr));
    }
}
int my_len3(const char* mystr) {
    //两个相邻char的地址差是1
    assert(mystr);
    const char* tmp = NULL;
    printf("mystr =  %p \n", mystr);

    tmp = mystr;
    printf(" before tmp =  %p\n", tmp);
    while (*(tmp) != '\0') 
    {
        tmp++;
    };
    printf(" after tmp =  %p \n", tmp);
    return tmp - mystr;

}
class Box {
public:
    Box() :m_height(0), m_width(0)
    {
        cout << "无参构造" << endl;
    }
    Box(const Box &b):m_height(b.m_height),m_width(b.m_width)
    {
        cout << "有参构造" << endl;
    }
    Box(const int h, const int w) 
    {
        this->m_height = h;
        this->m_width = w;
        cout << "调用了 （int h ，int w）" << endl;
    }
    Box operator+(const Box &b) 
    {
        this->m_height = this->m_height + b.m_height;
        this->m_width = this->m_width + b.m_width;
        cout << " 双目 +" << endl;
        return *this;
    }
    Box& operator=(const Box& other) 
    {
        if (this == &other) 
        {
            return *this;
        }
        cout << "拷贝赋值" << endl;
        this->m_height = other.m_height;
        this->m_width = other.m_width;
        return *this;
    }

    ~Box() 
    {
        cout << "执行析构" << endl;
    }
    int m_height;
    int m_width;
};
class String;
class String
{
public:
    char *m_str = NULL;
public:
    String() :m_str(NULL) {
        cout << "String 无参构造函数" << endl;
    };
    String(char *str);
    String(const String &str);
    String& operator=(const String& other);
    friend ostream& operator<<(ostream &out, String& s);
    ~String();
    
};

ostream& operator<<(ostream& out, String& s) {
    cout << "String.m_str:";
    out << s.m_str << endl;
    return out;
}
String::String(char* str) {
    int len = my_len1(str);
    this->m_str  = new char[len +1];
    my_strcpy(this->m_str, str);
}
String::String(const String& str) 
{
    int len = my_len1(str.m_str);
    this->m_str = new char[len + 1];
    my_strcpy(this->m_str, str.m_str);
}
String& String::operator=(const String& other) {
    if (this == &other) {
        return *this;
    }
    delete[] this->m_str;
    int len = my_len1(other.m_str);
    this->m_str = new char[len + 1];
    my_strcpy(this->m_str, other.m_str);
    cout << "拷贝赋值" << endl;
    return *this;
}
String::~String() {
    if (NULL != m_str) {
        delete[] m_str;
    }
}
int main(int argc, char** argv) {
#if 0
    cout << "init Box b1 b2 b3" << endl;
    Box b1(2, 3), b2(3, 2), b3;
    b3 = b1 + b2;
#else
    char arr[] = "abcd";
    cout << my_len1(arr) << endl;
    char arr1[] = "1234";
    char *res = my_strcpy(arr1, arr);
    cout << arr1 << endl;
    String s1(arr);
    String s2;
    s2 = s1;
    cout << s2 << endl;
#endif
    system("pause");
    return 0;
}