* 继承与派生 编程题＃1（Coursera 程序设计与算法 专项课程3 C++程序设计 郭炜、刘家瑛；OpenJudge）

编程题＃1

来源: POJ (http://cxsjsxmooc.openjudge.cn/test/5w5/)

注意： 总时间限制: 1000ms 内存限制: 65536kB

描述

写一个MyString 类，使得下面程序的输出结果是：

1. abcd-efgh-abcd-

2. abcd-

3.

4. abcd-efgh-

5. efgh-

6. c

7. abcd-

8. ijAl-

9. ijAl-mnop

10. qrst-abcd-

11. abcd-qrst-abcd- uvw xyz

about

big

me

take

abcd

qrst-abcd-

要求：MyString类必须是从C++的标准类string类派生而来。提示1：如果将程序中所有 “MyString” 用”string” 替换，那么题目的程序中除了最后两条语句编译无法通过外，其他语句都没有问题，而且输出和前面给的结果吻合。也就是说，MyString类对 string类的功能扩充只体现在最后两条语句上面。提示2: string类有一个成员函数 string substr(int start,int length); 能够求从 start位置开始，长度为length的子串

程序：

#include <iostream>
#include <cstring>
#include <cstdlib>
using namespace std;
// 在此处补充你的代码
int CompareString( const void * e1, const void * e2) {
MyString * s1 = (MyString * ) e1;
MyString * s2 = (MyString * ) e2;
if( *s1 < *s2 ) return -1;
else if( *s1 == *s2 ) return 0;
else if( *s1 > *s2 ) return 1;
}
int main() {
MyString s1("abcd-"),s2,s3("efgh-"),s4(s1);
MyString SArray[4] = {"big","me","about","take"};
cout << "1. " << s1 << s2 << s3<< s4<< endl;
s4 = s3; s3 = s1 + s3;
cout << "2. " << s1 << endl;
cout << "3. " << s2 << endl;
cout << "4. " << s3 << endl;
cout << "5. " << s4 << endl;
cout << "6. " << s1[2] << endl;
s2 = s1; s1 = "ijkl-";
s1[2] = 'A' ;
cout << "7. " << s2 << endl;
cout << "8. " << s1 << endl;
s1 += "mnop";
cout << "9. " << s1 << endl;
s4 = "qrst-" + s2;
cout << "10. " << s4 << endl;
s1 = s2 + s4 + " uvw " + "xyz";
cout << "11. " << s1 << endl;
qsort(SArray,4,sizeof(MyString), CompareString);
for( int i = 0;i < 4;++i )
cout << SArray[i] << endl;
//输出s1从下标0开始长度为4的子串
cout << s1(0,4) << endl;
//输出s1从下标为5开始长度为10的子串
cout << s1(5,10) << endl;
return 0;
}

输入

无

输出

1. abcd-efgh-abcd-

2. abcd-

3.

4. abcd-efgh-

5. efgh-

6. c

7. abcd-

8. ijAl-

9. ijAl-mnop

10. qrst-abcd-

11. abcd-qrst-abcd- uvw xyz

about

big

me

take

abcd

qrst-abcd-

样例输入

无

样例输出

1. abcd-efgh-abcd-
2. abcd-
3.
4. abcd-efgh-
5. efgh-
6. c
7. abcd-
8. ijAl-
9. ijAl-mnop
10. qrst-abcd-
11. abcd-qrst-abcd- uvw xyz
about
big
me
take
abcd
qrst-abcd-

程序解答：

#include <iostream>
#include <cstring>
#include <cstdlib>
using namespace std;

// 在此处补充你的代码
#include <string>
class MyString :public string{

public:
MyString() :string(){};                       //构造函数，针对 s2 初始化的默认
MyString(const char* str) :string(str){};     //构造函数，char*是数据类型，而string是类 http://www.cnblogs.com/GODYCA/archive/2013/01/08/2851923.html MyString(MyString &str) :string(str){};       //复制构造函数
MyString(const string &str) :string(str){};   //类型转换构造函数，把string类转换为MyString类

MyString operator()(int startPos, int strLengh){
return this->substr(startPos, strLengh);
}

/* 此处不用重载，在派生类对象中，包含着基类对象
friend ostream& operator<<(ostream& os, string& str){
os << str;
return os;
}
*/
};

int CompareString(const void * e1, const void * e2) {
MyString * s1 = (MyString *)e1;
MyString * s2 = (MyString *)e2;
if (*s1 < *s2)     return -1;
else if (*s1 == *s2) return 0;
else if (*s1 > *s2) return 1;
}
int main() {
MyString s1("abcd-"), s2, s3("efgh-"), s4(s1);
MyString SArray[4] = { "big", "me", "about", "take" };
cout << "1. " << s1 << s2 << s3 << s4 << endl;  //1. abcd-efgh-abcd-
s4 = s3;    s3 = s1 + s3;
cout << "2. " << s1 << endl;   //2. abcd-
cout << "3. " << s2 << endl;   //3.
cout << "4. " << s3 << endl;   //4. abcd-efgh-
cout << "5. " << s4 << endl;   //5. efgh-
cout << "6. " << s1[2] << endl;//6. c
s2 = s1;    s1 = "ijkl-";
s1[2] = 'A';
cout << "7. " << s2 << endl;   //7. abcd-
cout << "8. " << s1 << endl;   //8. ijAl-
s1 += "mnop";
cout << "9. " << s1 << endl;   //9. ijAl-mnop
s4 = "qrst-" + s2;
cout << "10. " << s4 << endl;  //10. qrst-abcd-
s1 = s2 + s4 + " uvw " + "xyz";
cout << "11. " << s1 << endl;  //11. abcd-qrst-abcd-uvw xyz

//以下才是重点*****************************************************
qsort(SArray, 4, sizeof(MyString), CompareString);
for (int i = 0; i < 4; ++i)
cout << SArray[i] << endl;  //about big me take
//输出s1从下标0开始长度为4的子串
cout << s1(0, 4) << endl;      //abcd
//输出s1从下标为5开始长度为10的子串
cout << s1(5, 10) << endl;     //qrst-abcd-
return 0;
}

其它解法参考： http://blog.csdn.net/nnnnnnnnnnnny/article/details/50366076

/*输出结果
#!#$####1. abcd-efgh-abcd-
@2. abcd-
3.
4. abcd-efgh-
5. efgh-
6. c
#7. abcd-
8. ijAl-
9. ijAl-mnop
@10. qrst-abcd-
@11. abcd-qrst-abcd- uvw xyz
about
big
me
take
%@abcd
%@qrst-abcd-
*/

#include <iostream>
#include <cstring>
#include <cstdlib>
using namespace std;
// 在此处补充你的代码
#include <string>
class MyString : public string
{
public:
MyString() :string() { cout << "!"; };
MyString(const string &str) :string(str) { cout << "@"; }; //类型转换构造函数
MyString(const char* str) :string(str) { cout << "#"; };//char*是数据类型，而string是类，要弄清楚。
MyString(MyString& myStr) :string(myStr) { cout << "$"; };//复制构造函数
//我们发现在派生类的拷贝构造函数中的初始化列表中，基类拷贝构造函数的参数是派生类，但是这样子是没有关系的，编译系统会自动将派生类缩减成基类规模（这是我的个人理解，进行缩减的只是派生类的临时对象，不会对参数进行修改），然后传入给基类的拷贝构造函数，然后在派生类的拷贝构造函数当中再将派生类比基类多出的成员变量进行拷贝。
MyString operator()(int start, int length)
{
cout << "%";
return this->substr(start, length);
};
};
int CompareString(const void * e1, const void * e2) {
MyString * s1 = (MyString *)e1;
MyString * s2 = (MyString *)e2;
if (*s1 < *s2)     return -1;
else if (*s1 == *s2) return 0;
else if (*s1 > *s2) return 1;
}
int main()
{
MyString s1("abcd-"), s2, s3("efgh-"), s4(s1);
MyString SArray[4] = { "big", "me", "about", "take" };
cout << "1. " << s1 << s2 << s3 << s4 << endl;
s4 = s3;
s3 = s1 + s3;//此处会调用string类型转换构造函数
cout << "2. " << s1 << endl;
cout << "3. " << s2 << endl;
cout << "4. " << s3 << endl;
cout << "5. " << s4 << endl;
cout << "6. " << s1[2] << endl;
s2 = s1;    s1 = "ijkl-";
s1[2] = 'A';
cout << "7. " << s2 << endl;
cout << "8. " << s1 << endl;
s1 += "mnop";
cout << "9. " << s1 << endl;
s4 = "qrst-" + s2;//此处会调用string类型转换构造函数
cout << "10. " << s4 << endl;
s1 = s2 + s4 + " uvw " + "xyz";
cout << "11. " << s1 << endl;
qsort(SArray, 4, sizeof(MyString), CompareString);
for (int i = 0; i < 4; ++i)
cout << SArray[i] << endl;
//输出s1从下标0开始长度为4的子串
cout << s1(0, 4) << endl;
//输出s1从下标为5开始长度为10的子串
cout << s1(5, 10) << endl;
return 0;
}