完成 MyString 类的实现，使程序正确运行 #include <iostream> #include <cstring> using namespace std; class MyString { public: // 无参构造函数 MyString(); // 构造函数，传入一个C语言风格字符串 MyString(const char *s); // 拷贝构造函数 MyString(const MyString &s); // 析构函数 ~MyString(); // 将C语言风格的字符串赋值给MyString对象 MyString& operator=(const char *s); // 将一个MyString对象赋值给另一个MyString对象 MyString& operator=(const MyString &s); // 将这个MyString对象与C语言风格的字符串相连 MyString& operator+=(const char *s); // 将这个MyString对象与另一个MyString对象相连 MyString& operator+=(const MyString &s); // 返回下标为pos的字符 char& operator[](int pos); // 返回子串 [pos, pos+count) // 若请求的子串越过字符串的结尾，即count大于size() - pos，则返回的子串为[pos, size()) // 若pos不在字符串的下标范围内，返回空的MyString对象 // 若count == -1，返回子串[pos, size()) MyString substr(int pos = 0, int count = -1); // 字符串的长度 int size() const; // 返回C语言风格的字符串 const char* c_str() const; private: char *m_buf; int m_size; }; // 请在此处填写 int main() { char s[101]; cin.getline(s, 101); int pos, count; // 创建、拷贝、赋值 MyString s1(s), s2(s1), s3, s4, s5; s3 = s; s4 = s1; cout << "s1: " << s1.c_str() << endl; cout << "s2: " << s2.c_str() << endl; cout << "s3: " << s3.c_str() << endl; cout << "s4: " << s4.c_str() << endl; // 拼接 s3 += s; s4 += s1; cout << "s3 += s: " << s3.c_str() << endl; cout << "s4 += s1: " << s4.c_str() << endl; // 下标 cin >> pos; s4[pos] = 'm'; cout << "s4[pos] = 'm': " << s4.c_str() << endl; // 取子串 cin >> pos >> count; s5 = s4.substr(pos, count); cout << "s5: " << s5.c_str() << endl; // 以后还可以重载<<直接输出一个MyString对象哦 TODO return 0; }

实现如下：

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

class MyString {
public:
    // 无参构造函数
    MyString() : m_buf(nullptr), m_size(0) {}
    // 构造函数，传入一个C语言风格字符串
    MyString(const char *s) : m_buf(nullptr), m_size(0) {
        if (s != nullptr) {
            m_size = strlen(s);
            m_buf = new char[m_size + 1];
            strcpy(m_buf, s);
        }
    }
    // 拷贝构造函数
    MyString(const MyString &s) : m_buf(nullptr), m_size(s.m_size) {
        if (m_size > 0) {
            m_buf = new char[m_size + 1];
            strcpy(m_buf, s.m_buf);
        }
    }
    // 析构函数
    ~MyString() {
        delete[] m_buf;
    }
    // 将C语言风格的字符串赋值给MyString对象
    MyString& operator=(const char *s) {
        if (s == nullptr) {
            delete[] m_buf;
            m_buf = nullptr;
            m_size = 0;
        }
        else {
            int len = strlen(s);
            if (len > m_size) {
                delete[] m_buf;
                m_buf = new char[len + 1];
                m_size = len;
            }
            strcpy(m_buf, s);
        }
        return *this;
    }
    // 将一个MyString对象赋值给另一个MyString对象
    MyString& operator=(const MyString &s) {
        if (this != &s) {
            if (s.m_buf == nullptr) {
                delete[] m_buf;
                m_buf = nullptr;
                m_size = 0;
            }
            else {
                int len = s.m_size;
                if (len > m_size) {
                    delete[] m_buf;
                    m_buf = new char[len + 1];
                    m_size = len;
                }
                strcpy(m_buf, s.m_buf);
            }
        }
        return *this;
    }
    // 将这个MyString对象与C语言风格的字符串相连
    MyString& operator+=(const char *s) {
        int len = strlen(s);
        char *new_buf = new char[m_size + len + 1];
        if (m_buf != nullptr) {
            strcpy(new_buf, m_buf);
            delete[] m_buf;
        }
        strcpy(new_buf + m_size, s);
        m_buf = new_buf;
        m_size += len;
        return *this;
    }
    // 将这个MyString对象与另一个MyString对象相连
    MyString& operator+=(const MyString &s) {
        return (*this += s.c_str());
    }
    // 返回下标为pos的字符
    char& operator[](int pos) {
        return m_buf[pos];
    }
    // 返回子串 [pos, pos+count)
    // 若请求的子串越过字符串的结尾，即count大于size() - pos，则返回的子串为[pos, size())
    // 若pos不在字符串的下标范围内，返回空的MyString对象
    // 若count == -1，返回子串[pos, size())
    MyString substr(int pos = 0, int count = -1) {
        if (pos < 0 || pos >= m_size) {
            return MyString();
        }
        if (count == -1) {
            count = m_size - pos;
        }
        else if (count > m_size - pos) {
            count = m_size - pos;
        }
        char *new_buf = new char[count + 1];
        strncpy(new_buf, m_buf + pos, count);
        new_buf[count] = '\0';
        MyString res(new_buf);
        delete[] new_buf;
        return res;
    }
    // 字符串的长度
    int size() const {
        return m_size;
    }
    // 返回C语言风格的字符串
    const char* c_str() const {
        return m_buf;
    }
private:
    char *m_buf;
    int m_size;
};

int main() {
    char s[101];
    cin.getline(s, 101);
    int pos, count;

    // 创建、拷贝、赋值
    MyString s1(s), s2(s1), s3, s4, s5;
    s3 = s;
    s4 = s1;
    cout << "s1: " << s1.c_str() << endl;
    cout << "s2: " << s2.c_str() << endl;
    cout << "s3: " << s3.c_str() << endl;
    cout << "s4: " << s4.c_str() << endl;

    // 拼接
    s3 += s;
    s4 += s1;
    cout << "s3 += s: " << s3.c_str() << endl;
    cout << "s4 += s1: " << s4.c_str() << endl;

    // 下标
    cin >> pos;
    s4[pos] = 'm';
    cout << "s4[pos] = 'm': " << s4.c_str() << endl;

    // 取子串
    cin >> pos >> count;
    s5 = s4.substr(pos, count);
    cout << "s5: " << s5.c_str() << endl;

    return 0;
}