c++ 编程练习 014:MyString

北大程序设计与算法（三）测验题汇总(2020春季)

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描述

补足MyString类，使程序输出指定结果

#include <iostream>
#include <string>
#include <cstring>
using namespace std;
class MyString {
	char * p;
public:
	MyString(const char * s) {
		if( s) {
			p = new char[strlen(s) + 1];
			strcpy(p,s);
		}
		else
			p = NULL;

	}
	~MyString() { if(p) delete [] p; }
// 在此处补充你的代码
};
int main()
{
	char w1[200],w2[100];
	while( cin >> w1 >> w2) {
		MyString s1(w1),s2 = s1;
		MyString s3(NULL);
		s3.Copy(w1);
		cout << s1 << "," << s2 << "," << s3 << endl;

		s2 = w2;
		s3 = s2;
		s1 = s3;
		cout << s1 << "," << s2 << "," << s3 << endl;
		
	}
}

输入
多组数据，每组一行，是两个不带空格的字符串

输出
对每组数据，先输出一行，打印输入中的第一个字符串三次,然后再输出一行，打印输入中的第二个字符串三次

样例输入
abc def
123 456

样例输出
abc,abc,abc
def,def,def
123,123,123
456,456,456

来源
Guo Wei

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分析

MyString s1(w1)需要构造函数，题目已经给出；
MyString s2 = s1需要复制构造函数；
s2 = w2;需要临时构造函数；
s3 = s2;s1 = s3;需要等号运算符的重载；

---

解答

void Copy(const char * s){
		if(p)
			delete []p;
		if(s){
			p = new char[strlen(s) + 1];
			strcpy(p,s);
		}
		else
			p = NULL;
	}
	friend ostream &operator<<(ostream &o,const MyString & s){
		o << s.p;
		return o;
	}
	MyString (const MyString & s) {
		if( s.p ) {
			p = new char[strlen(s.p)+1];
			strcpy(p,s.p);
		}
		else {
			p = NULL;
		}
	}
	MyString &operator = (const MyString & s){
		if(this == &s)
			return *this;
		if(s.p)
		{
			if(p)
				delete []p;
			p = new char[strlen(s.p) + 1];
			strcpy(p,s.p);
		}
		else
			p = NULL;
		return *this;
	}

执行效果