【C++面向对象练习】实现简单的string

程序设计与算法（三) 019 全面的MyString
学C++的过程中，每看到自己前一天写的代码，都会感觉这是什么gs玩意。。

//
// Created by vv123 on 2022/3/22.
//
#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
{
    char* str = NULL;
public:
    MyString(): str(new char[1]) { str[0] = 0; }
    MyString(const char* s) {
        delete[] str;
        str = new char[strlen(s) + 1];
        strcpy(str, s);
    }
    MyString(const MyString& s) {
        delete[] str;
        str = new char[strlen(s.str) + 1];
        strcpy(str, s.str);
    }
    MyString& operator=(const char* s) {
        delete[] str;
        str = new char[strlen(s) + 1];
        strcpy(str, s);
        return *this;
    }
    MyString& operator=(const MyString& s) {
        if (&s == this) return *this;
        if (str) delete[] str;
        str = new char[strlen(s.str) + 1];
        strcpy(str, s.str);
        return *this;
    }
    MyString operator+ (const MyString& s) {
        MyString res;
        res.str = new char[strlen(str) + strlen(s.str) + 1];
        strcpy(res.str, str);
        strcat(res.str, s.str);
        return res;
    }
    friend MyString operator+(const char* str, const MyString& s) {
        MyString res;
        res.str = new char[strlen(str) + strlen(s.str) + 1];
        strcpy(res.str, str);
        strcat(res.str, s.str);
        return res;
    }
    MyString& operator+=(const char* s) {
        strcat(str, s);
        return *this;
    }
    char& operator[](int i) {
        return str[i];
    }
    char* operator()(int pos, int len) {
        char* res = new char[len + 1];
        for (int i = 0; i < len; i++)
            res[i] = str[pos + i];
        res[len] = '\0';
        return res;
    }
    bool operator<(const MyString& s) {
        return strcmp(str, s.str) < 0;
    }
    bool operator>(const MyString& s) {
        return strcmp(str, s.str) > 0;
    }
    bool operator==(const MyString& s) {
        return strcmp(str, s.str) == 0;
    }
    friend ostream& operator<<(ostream& os, const MyString& s) {
        os << s.str;
        return os;
    }
    ~MyString() { delete[] str; }
};



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;
}