main.cpp

#include <cstdlib>
#include <iostream>

using namespace std;
#if 0
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);
}
#endif

class MyString {
// Your Code Here
public:
    MyString() = default;
    MyString(MyString const &x) {
        ptr = nullptr;
        copyWithCheck(x.ptr);
    }
    MyString(void const *p) {
        ptr = nullptr;
        copyWithCheck(static_cast<char const *>(p));
    }
    ~MyString() {
        delete[]ptr;
    }
    bool operator<(MyString const &a) const {
        return ::strcmp(ptr, a.ptr) < 0;
    }
    bool operator==(MyString const &a) const {
        return ::strcmp(ptr, a.ptr) == 0;
    }
    bool operator>(MyString const &a) const {
        return a < *this;
    }
    MyString &operator=(MyString const &a) {
        copyWithCheck(a.ptr);
        return *this;
    }
    MyString operator+(MyString const &a) const {
        MyString ret;
        auto leftLen = ::strlen(ptr);
        auto rightLen = ::strlen(a.ptr);
        auto newSpc = new char[leftLen + rightLen + 1];
        memset(newSpc, 0, sizeof(char) * (leftLen + rightLen + 1));
        ::strcat(newSpc, ptr);
        ::strcat(newSpc, a.ptr);
        ret.ptr = newSpc;
        return ret;
    }
    MyString &operator+=(MyString const &a) {
        *this = *this + a;
        return *this;
    }
    MyString operator()(size_t start, size_t length) const {
        MyString ret(ptr + start);
        ret.ptr[length + 1] = '\0';
        return ret;
    }
    char &operator[](size_t n) const {
        return ptr[n];
    }
    friend ostream &operator<<(ostream &os, MyString const &a) {
        if (a.ptr == nullptr) { return os; };
        return os << a.ptr;
    }
    friend MyString operator+(char const *x, MyString const &a) {
        return MyString(x) + a;
    }
private:
    char *ptr;
    void copyWithCheck(const char *src) {
        auto newLen = ::strlen(src);
        if (ptr != nullptr) {
            auto currLen = ::strlen(ptr);
            if (currLen < newLen) {
                delete[]ptr;
                ptr = new char[newLen + 1];
            }
        } else {
            ptr = new char[newLen + 1];
        }
        memset(ptr, 0, sizeof(char) * (newLen + 1));
        ::strcpy(ptr, src);
    }
    static void memset(void *dst, char obj, size_t sz) {
        auto charDst = static_cast<char *>(dst);
        while (sz-- > 0) {
            *charDst++ = obj;
        }
    }
// Your Code Ends Here
};


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() {
    char *a = nullptr;
    cout << *a << endl;
    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;
}