C++面向对象学习:全面的MyString

前言

今天完成到第五周的任务了，课程也终于学完了一半了。

不得不说，学习了面向对象之后，感觉对于c++的构成有了更加深入的了解。之前很多没有搞懂的原理在学了之后感觉其实也挺简单的。感觉设计者的思路真的很巧妙啊。

题目链接

题目有一点繁琐，就是各种各样的重载操作。没有什么好说的。

不过在做题目的时候，还是遇到了几个问题:

strlen 不能够去求指针NULL的长度，cout 输出字符也是以’\0’ 结尾的，所以不能输出NULL。
感觉如果在大程序之中，如果在调用返回的时候都构造一个新的对象 程序应该比较慢。

代码

#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
{
    public:
        int Len;
        char *Sequnece;
        MyString(const char *s=NULL){
            if (s){
                Len = strlen(s);
                Sequnece = new char [Len+1];
                strcpy(Sequnece, s);
            }
            else {
                Len = 0;
                Sequnece = NULL;
            }
        }
        MyString(const MyString & s){
            if (s.Len){
                Len = s.Len;
                Sequnece = new char [Len+1];
                strcpy(Sequnece, s.Sequnece);
            }
            else {
                Len = 0;
                Sequnece = NULL;
            }
        }
        ~MyString(){
            delete []Sequnece;
        }
        MyString & operator=(const MyString &s){
            if (s.Sequnece == Sequnece) return *this;
            if (s.Len){
                delete []Sequnece;
                Len = s.Len;
                Sequnece = new char [Len+1];
                strcpy(Sequnece, s.Sequnece);
            }
            else {
                Len = 0;
                Sequnece = NULL;
            }
            return *this;
        }
        MyString operator+(const MyString &s){
            MyString ss;
            ss.Len = Len + s.Len;
            ss.Sequnece = new char[ss.Len+1];
            strcpy(ss.Sequnece, Sequnece);
            strcat(ss.Sequnece, s.Sequnece);
            return ss;
        }
        MyString & operator+=(const MyString &s){
            char *ss = new char [Len+1];
            strcpy(ss, Sequnece);
            delete []Sequnece;
            Len = Len + s.Len;
            Sequnece = new char [Len+1];
            strcpy(Sequnece, ss);
            strcat(Sequnece, s.Sequnece);
            return *this;
        }
        char* operator()(int t,int l){
            char *s = new char [l+1];
            int sp = 0;
            for (int i = t; i < t + l; i++) s[sp++] = Sequnece[i];
            s[sp]=0;
            return s;
        }
        char &operator[](const int &i){
            return Sequnece[i];
        }
        friend ostream & operator<<(ostream & o,const MyString & s){
            if (s.Len) o<<s.Sequnece;
            return o;
        }
        friend MyString operator+(const char *l,const MyString & r){
            MyString ss;
            ss.Len = strlen(l) + r.Len;
            ss.Sequnece = new char[ss.Len+1];
            strcpy(ss.Sequnece, l);
            strcat(ss.Sequnece, r.Sequnece);
            return ss;
        }
        friend int operator<(const MyString &l,const MyString &r){
            int f = strcmp(l.Sequnece, r.Sequnece);
            if (f == -1) return 1;
            return 0;
        }
        friend int operator==(const MyString &l,const MyString &r){
            int f = strcmp(l.Sequnece, r.Sequnece);
            if (f == 0) return 1;
            return 0;
        }
        friend int operator>(const MyString &l,const MyString &r){
            int f = strcmp(l.Sequnece, r.Sequnece);
            if (f == 1) return 1;
            return 0;
        }
};


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<< "\n";
    s4 = s3;
    s3 = s1 + s3;
    cout << "2. " << s1 << "\n";
    cout << "3. " << s2 << "\n";
    cout << "4. " << s3 << "\n";
    cout << "5. " << s4 << "\n";
    cout << "6. " << s1[2] << "\n";
    s2 = s1;
    s1 = "ijkl-";
    s1[2] = 'A' ;
    cout << "7. " << s2 << "\n";
    cout << "8. " << s1 << "\n";
    s1 += "mnop";
    cout << "9. " << s1 << "\n";
    s4 = "qrst-" + s2;
    cout << "10. " << s4 << "\n";
    s1 = s2 + s4 + " uvw " + "xyz";
    cout << "11. " << s1 << "\n";
    qsort(SArray,4,sizeof(MyString),CompareString);
    for( int i = 0;i < 4;i ++ )
    cout << SArray[i] << "\n";
    //s1的从下标0开始长度为4的子串
    cout << s1(0,4) << "\n";
    //s1的从下标5开始长度为10的子串
    cout << s1(5,10) << "\n";
    return 0;
}

赏

谢谢你请我吃糖果