大连理工大学C语言题目（十）

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设计字符串类 myString，若有 myString 类对象 s1、s2 和 s3，重载运算符实现如下操作： 1）重载“＋”实现字符串连接功能，使表达式 s1= s2+s3 成立； 2）重载“<”判断两个字符串的大小，如 if(s1 < s2) cout<<s1<<”<”<<s2； 3）重载“<<”与“>>”，实现字符串的输入与输出操作，如 cin>>s2; cout<<s2<<endl; 4）重载运算符“()”，从字符串对象中返回一个子串。如 s1(2,4)表示返回从子串，即从 s[2](s1 第 3 个字符)开始的子串(包括 s1[2]、s1[3]和 s1[4]三个字符)。
5）重载运算符[]，获取下标为 i 的字符，并可以执行对该字符赋值的操作； 6) 重载运算符=，实现字符串对象的赋值操作。

#include <iostream>
#include<cstring>

using namespace std;

class myString
{
public:
	myString(int size, const char*);
	myString();
	~myString();
	myString(const myString&);
	myString operator+(myString&);
	bool operator<(myString&);
	friend ostream& operator<<(ostream&, const myString&);
	friend istream& operator>>(istream&, myString&);
	myString operator()(int, int);
	myString& operator[](int);
	myString& operator=(const myString&);
private:
	int length;
	char* s;
};

myString::myString(int size, const char* s1) :length(size)
{
	s = new char[length + 1]();
	strcpy(s, s1);
}

myString::myString()
{
	length = 0;
	s = new char[length + 1]();
}

myString::~myString()
{
	delete[]s;
	s = nullptr;
}

myString::myString(const myString&s1) {
	length = s1.length;
	s = new char[length + 1]();
	strcpy(s, s1.s);
}

myString myString::operator+(myString& s1) {
	myString S(length + s1.length, s);
	strcat(S.s, s1.s);
	return S;
}

bool myString::operator<(myString& s1) {
	if (strcmp(s, s1.s) >= 0)
	{
		return false;
	}
	else
	{
		return true;
	}
}

ostream& operator<<(ostream& os, const myString& s1) {
	os << s1.s << endl;
	return os;
}

istream& operator>>(istream& is, myString& s1) {
	cout << "length:";
	is >> s1.length;
	if (s1.s!=NULL)
	{
		delete[]s1.s;
	}
	s1.s = new char[s1.length+1]();
	cout << "string:";
	is >> s1.s;
	return is;
}

myString myString::operator()(int j, int k) {
	myString s1(k - j + 1, "");
	for (int i = 0; i < k - j + 1; i++)
	{
		s1.s[i] = s[j + i];
	}

	return s1;
}

myString& myString::operator[](int i) {
	cout << "You are goning to change it as:" << endl;
	cin >> s[i];
	return *this;
}

myString& myString::operator=(const myString& s1) {
	length = s1.length;
	if (s!=NULL)
	{
		delete[]s;
	}
	s = new char[length + 1];
	strcpy(s, s1.s);
	return*this;
}

int main()
{
	myString s1(5, "zhang"), s2(2, "li"), s3;
	cin >> s3;
	cout << s3;
	cout << s1 << s2 << s3;
	s3 = s1 + s2;
	cout << s3;
	if (s1 < s2)
	{
		cout << s1 << "<" << s2;
	}
	myString s5 = s1(2, 4);
	cout << s5;
	cout << s2[1];
	return 0;
}