【C++ Primer Plus习题】12.1

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问题:

解答:
main.cpp

#include <iostream>
#include "Cow.h"
using namespace std;

int main()
{
	Cow c1;
	Cow c2("老母牛", "喝奶", 200);
	Cow c3(c2);
	c1 = c3;
	c1.ShowCow();
	cout << endl;
	c2.ShowCow();
	cout << endl;
	c3.ShowCow();
	cout << endl;
	return 0;
}

Cow.h

#pragma once
#include <iostream>
using namespace std;
class Cow
{
	char name[20];
	char* hobby;
	double weight;

public:
	Cow();
	Cow(const char*nm,const char*ho,double wt);
	Cow(const Cow &c);
	~Cow();
	Cow& operator=(const Cow& c);
	void ShowCow()const;
};

Cow.cpp

#include "Cow.h"

Cow::Cow()
{
	name[0] = '\0';
	hobby = NULL;
	weight = 0;
}
Cow::Cow(const char* nm, const char* ho, double wt)
{
	if ((strcpy_s(name, 20, nm)))cout << "复制失败原字符太长!" << endl;
	hobby = new char[strlen(ho)+1];
	strcpy_s(hobby, strlen(ho) + 1, ho);
	weight = wt;
}
Cow::Cow(const Cow&c)
{
	strcpy_s(name,20, c.name);
	hobby = new char[strlen(c.hobby) + 1];
	strcpy_s(hobby, strlen(c.hobby) + 1, c.hobby);
	weight = c.weight;
}
Cow::~Cow()
{
	delete[] hobby;
}
Cow& Cow::operator=(const Cow& c)
{
	if (this == &c)
	{
		return *this;
	}
	if (hobby)delete[] hobby;

	strcpy_s(name, 20, c.name);
	hobby = new char[strlen(c.hobby) + 1];
	strcpy_s(hobby, strlen(c.hobby) + 1, c.hobby);
	weight = c.weight;
	return *this;
}
void Cow::ShowCow()const
{
	if (hobby == NULL)
	{
		cout << "母牛的信息为空!" << endl;
		return;
	}
	cout << "母牛的名字为:" << name << endl;
	cout << "母牛的嗜好为:" << hobby << endl;
	cout << "母牛的体重为:" << weight << endl;
}

运行结果:

考查点:

• 默认构造函数
  
• 自定义构造函数
  
• 拷贝构造函数
  
• 赋值构造函数
  
• 动态内存分配
  

注意:

• strcpy_s复制成功的返回值为0
  

• strlen是得到字符串不带’\0’的长度,所以我们分配内存时需要加1

  

• 赋值构造函数返回的是引用用于连等
  

• 如果对象自己赋值自己就可以直接返回.如果原来指针不为空的需要清除
  

• 析构函数避免内存泄漏
  

2024年9月7日19:48:10