基于char* 设计一个字符串类MyString，具有构造函数、析构函数、复制构造函数。具体如下： MyString(); MyString(const char* cString); char at(int index) const; int length() const; void clear(); bool empty() const; int compare(const MyString& s) const; int compare(int index, int n, const MyString& s) const; void copy(char s[], int index , int n); char* data() const; int find(char ch) const ; int find(char ch ,int index) const; int find(const MyString& s, int index) const; 另外，还有append、assign、substr、erase函数，详见11.14和11.15要求。

好的，下面是一个可能的实现代码：

#include <iostream>
#include <cstring>
using namespace std;

class MyString {
private:
    char* str;
    int len;
public:
    MyString() : len(0), str(nullptr) {}
    MyString(const char* cString) : len(strlen(cString)), str(new char[len + 1]) {
        strcpy(str, cString);
    }
    MyString(const MyString& other) : len(other.len), str(new char[len + 1]) {
        strcpy(str, other.str);
    }
    ~MyString() {
        if (str != nullptr)
            delete[] str;
    }
    char at(int index) const {
        if (index < 0 || index >= len)
            throw "Index out of range";
        return str[index];
    }
    int length() const {
        return len;
    }
    void clear() {
        if (str != nullptr) {
            delete[] str;
            str = nullptr;
        }
        len = 0;
    }
    bool empty() const {
        return len == 0;
    }
    int compare(const MyString& s) const {
        return strcmp(str, s.str);
    }
    int compare(int index, int n, const MyString& s) const {
        if (index < 0 || index >= len || n < 0 || n > len - index)
            throw "Invalid index or length";
        return strncmp(str + index, s.str, n);
    }
    void copy(char s[], int index, int n) {
        if (index < 0 || index >= len || n < 0 || n > len - index)
            throw "Invalid index or length";
        strncpy(s, str + index, n);
    }
    char* data() const {
        return str;
    }
    int find(char ch) const {
        return find(ch, 0);
    }
    int find(char ch, int index) const {
        if (index < 0 || index >= len)
            throw "Invalid index";
        char* p = strchr(str + index, ch);
        if (p == nullptr)
            return -1;
        else
            return p - str;
    }
    int find(const MyString& s, int index) const {
        if (index < 0 || index >= len)
            throw "Invalid index";
        char* p = strstr(str + index, s.str);
        if (p == nullptr)
            return -1;
        else
            return p - str;
    }
    MyString& append(const MyString& other) {
        int newLen = len + other.len;
        char* newStr = new char[newLen + 1];
        strcpy(newStr, str);
        strcat(newStr, other.str);
        if (str != nullptr)
            delete[] str;
        str = newStr;
        len = newLen;
        return *this;
    }
    MyString& assign(const MyString& other) {
        if (this == &other)
            return *this;
        if (str != nullptr)
            delete[] str;
        len = other.len;
        str = new char[len + 1];
        strcpy(str, other.str);
        return *this;
    }
    MyString substr(int index, int n) const {
        if (index < 0 || index >= len || n < 0 || n > len - index)
            throw "Invalid index or length";
        char subStr[n + 1];
        strncpy(subStr, str + index, n);
        subStr[n] = '\0';
        return MyString(subStr);
    }
    MyString& erase(int index, int n) {
        if (index < 0 || index >= len || n < 0 || n > len - index)
            throw "Invalid index or length";
        char* newStr = new char[len - n + 1];
        strncpy(newStr, str, index);
        strncpy(newStr + index, str + index + n, len - index - n);
        newStr[len - n] = '\0';
        if (str != nullptr)
            delete[] str;
        str = newStr;
        len -= n;
        return *this;
    }
};

int main() {
    MyString s1("Hello");
    cout << s1.length() << endl;                // 5
    cout << s1.at(1) << endl;                   // 'e'
    s1.clear();
    cout << s1.empty() << endl;                  // 1
    MyString s2("World");
    cout << s2.compare(MyString("World")) << endl;  // 0
    cout << s2.compare(1, 3, MyString("orl")) << endl;  // 0
    char s[10];
    s2.copy(s, 1, 3);
    s[3] = '\0';
    cout << s << endl;                          // "orl"
    cout << s2.data() << endl;                  // "World"
    cout << s2.find('r') << endl;               // 2
    cout << s2.find('r', 3) << endl;            // 3
    cout << s2.find(MyString("rl")) << endl;    // 2
    s2.append(MyString("!"));
    cout << s2.data() << endl;                  // "World!"
    s2.assign(MyString("Hello"));
    cout << s2.data() << endl;                  // "Hello"
    MyString s3 = s2.substr(1, 3);
    cout << s3.data() << endl;                  // "ell"
    s2.erase(1, 3);
    cout << s2.data() << endl;                  // "Ho"
    return 0;
}

这个 `MyString` 类中，包含了一个字符指针和一个整数，分别用 `str` 和 `len` 表示。构造函数、复制构造函数和析构函数都有实现。每个成员函数都有一些基本的字符串操作，例如访问指定位置的字符、获取字符串长度、清空字符串、比较字符串、查找指定字符或子串、拷贝指定长度的子串、获取字符串的指针、在末尾追加字符串、替换为指定字符串的拷贝、获取子串等等。在主函数中，使用这些函数进行了一些操作，以便验证它们的正确性。