C++面向对象程序设计 019:全面的MyString ---- (北大Mooc)

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原题题目

#include <cstdlib>
#include <iostream>
using namespace std;
int strlen(const char * s) 
{
    
    	int i = 0;
	for(; s[i]; ++i);
	return i;
}
void strcpy(char * d,const char * s)
{
    
    
	int i = 0;
	for( i = 0; s[i]; ++i)
		d[i] = s[i];
	d[i] = 0;
		
}
int strcmp(const char * s1,const char * s2)
{
    
    
	for(int i = 0; s1[i] && s2[i] ; ++i) {
    
    
		if( s1[i] < s2[i] )
			return -1;
		else if( s1[i] > s2[i])
			return 1;
	}
	return 0;
}
void strcat(char * d,const char * s)
{
    
    
	int len = strlen(d);
	strcpy(d+len,s);
}
class MyString
{
    
    
// 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;
	//s1的从下标0开始长度为4的子串
	cout << s1(0,4) << endl;
	//s1的从下标5开始长度为10的子串
	cout << s1(5,10) << endl;
	return 0;
}

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代码实现

    char* str;
// 在此处补充你的代码
public:
MyString()
{
    
    
    str = new char[1];
    str[0] = '\0';
}

MyString(const char* a)
{
    
    
    str = new char[strlen(a)+1];
    strcpy(str,a);
}

MyString(const MyString& a)
{
    
    
    str = new char[strlen(a.str)+1];
    strcpy(str,a.str);
}

~MyString()
{
    
    
    if(str)
        delete []str;
}

friend ostream& operator<<(ostream& os,const MyString& a)
{
    
    
    os<<a.str;
    return os;
}

MyString& operator = (const MyString& a)
{
    
    
    delete []str;
    str = new char[strlen(a.str)+1];
    strcpy(str,a.str);
    return *this;
}

MyString operator +(MyString & a)
{
    
    
    MyString ret;
    ret.str = new char[strlen(str)+strlen(a.str)+1];
    int str1 = strlen(str),str2 = strlen(a.str);
    for(int i=0;i<str1+str2+1;i++)
        ret.str[i] = '\0';
    strcpy(ret.str,str);
    strcat(ret.str,a.str);
    return ret;
}

MyString operator + (const char* s)
{
    
    
    MyString ret;
    ret.str = new char[strlen(s)+strlen(str)+1];
    int str1 = strlen(s),str2 = strlen(str);
    for(int i=0;i<str1+str2+1;i++)
        ret.str[i] = '\0';
    strcpy(ret.str,str);
    strcat(ret.str,s);
    return ret;
}

friend MyString operator +(const char* s,const MyString& a)
{
    
    
    MyString ret;
    ret.str = new char[strlen(s)+strlen(a.str)+1];
    int str1 = strlen(s),str2 = strlen(a.str);
    for(int i=0;i<str1+str2+1;i++)
        ret.str[i] = '\0';
    strcpy(ret.str,s);
    strcat(ret.str,a.str);
    return ret;
}

char& operator[](int n)
{
    
    
    return str[n];
}

void operator+=(const char* s)
{
    
    
    strcat(str,s);
}

int operator<(const MyString& a)
{
    
    
    return str[0]<a.str[0];
}

int operator==(const MyString& a)
{
    
    
    return str[0]==a.str[0];
}

int operator>(const MyString& a)
{
    
    
    return str[0]>a.str[0];
}

MyString operator()(int tempstart,int tempend)
{
    
    
    MyString ret;
    ret = new char[tempend+1];
    for(int i=0;i<tempend;i++)
        ret[i] = '\0';
    strcpy(ret.str,str+tempstart);
    ret.str[tempend] = '\0';
    return ret;
}