构造、拷贝（复制）构造、赋值构造以及析构

#include<iostream>
using namespace std;

class Human
{
public:
Human(){ cout << "construct : " << ++human_num << endl; }
Human(const Human &){ cout << "copy: " << ++human_num << endl; }
Human &operator=(const Human &){ cout << "assign: " << ++human_num << endl; return *(new Human); }
~Human(){ cout << "destruct: " << --human_num << endl; }

static int human_num;
};

int Human::human_num = 0;

Human f1(Human x)
{
cout << "2--------" << endl;

return x;

cout << "3--------" << endl;
}

void main()
{
Human h1;//调用构造函数，human_num = 1;
cout << "1--------" << endl;

Human h2 = f1(h1);//拆分来看，a.先看表达式右值，右值为一个函数，并且是值传递，调用拷贝构造函数，human_num = 2，
//b.然后紧接着看表达式左值，调用拷贝构造函数，将f1返回的临时变量赋给h2，human_num = 3,
//c.最后，退出f1函数时，销毁x，调用析构函数，human_num = 2;注意b和c执行的顺序;
cout << "4--------" << endl;

//退出main函数，先析构h2, human_num = 1, 再析构h1, human_num = 0;

//思考以下代码
//Human h1;
//cout << "1--------" << endl;

//Human h2;
//h2 = f1(h1);//此处为赋值构造，分析更为繁琐
//cout << "4--------" << endl;
}

#include <iostream>
#include <assert.h>
using namespace std;

class String
{
public:
String(const char *str = NULL);//构造函数
String(const String &other);//拷贝构造函数
String &operator=(const String &other);//赋值构造函数
~String(void);//析构函数

private:
char *m_data;//用于保留字符串
};

String::~String(void)
{
//delete m_data;
delete[]m_data;
}

String::String(const char *str)
{
if (NULL == str)
{
m_data = new char[1];
assert(m_data != NULL);
*m_data = '\0';
}
else
{
int length = strlen(str);
m_data = new char[length + 1];
assert(m_data != NULL);
strcpy(m_data, str);
}
}

String::String(const String &other)
{
int length = strlen(other.m_data);
m_data = new char[length + 1];
assert(m_data != NULL);
strcpy(m_data, other.m_data);
}

String &String::operator=(const String &other)
{
//1.自检查赋值
if (this == &other)
return *this;
//2.释放原有的内存资源
delete[]m_data;
//3.分配新的内存资源，并复制内容
int length = strlen(other.m_data);
m_data = new char[length + 1];
assert(m_data != NULL);
strcpy(m_data, other.m_data);
//4.返回本对象的引用
return *this;
}