完成下列的 String 类，并在主函数 main( )中测试它。 class String { public: String(const char *str = NULL); // constructor String(const String &other); // copy constructor ~ String(void); // destructor String & operate =(char *str); String & operate =(const String &other);// 重载=运算符 int operator==(String &other); // 重载==运算符 int operator==(char *str); private: char *m_data; // used for storing the string int length; };

下面是 String 类的实现：

#include <cstring>

class String {
public:
    String(const char* str = NULL);
    String(const String& other);
    ~String();
    String& operator=(const char* str);
    String& operator=(const String& other);
    int operator==(String& other);
    int operator==(const char* str);

private:
    char* m_data;
    int length;
};

String::String(const char* str) {
    if (str == NULL) {
        length = 0;
        m_data = new char[1];
        m_data[0] = '\0';
    }
    else {
        length = strlen(str);
        m_data = new char[length + 1];
        strcpy(m_data, str);
    }
}

String::String(const String& other) {
    length = other.length;
    m_data = new char[length + 1];
    strcpy(m_data, other.m_data);
}

String::~String() {
    delete[] m_data;
}

String& String::operator=(const char* str) {
    if (m_data == str) {
        return *this;
    }

    delete[] m_data;
    if (str == NULL) {
        length = 0;
        m_data = new char[1];
        m_data[0] = '\0';
    }
    else {
        length = strlen(str);
        m_data = new char[length + 1];
        strcpy(m_data, str);
    }

    return *this;
}

String& String::operator=(const String& other) {
    if (m_data == other.m_data) {
        return *this;
    }

    delete[] m_data;
    length = other.length;
    m_data = new char[length + 1];
    strcpy(m_data, other.m_data);

    return *this;
}

int String::operator==(String& other) {
    return strcmp(m_data, other.m_data) == 0;
}

int String::operator==(const char* str) {
    return strcmp(m_data, str) == 0;
}

在主函数中可以这样测试：

#include <iostream>

int main() {
    String str1("hello");
    String str2("world");
    String str3(str1);

    std::cout << "str1 = " << str1 << std::endl;
    std::cout << "str2 = " << str2 << std::endl;
    std::cout << "str3 = " << str3 << std::endl;

    str2 = str1;
    std::cout << "After str2 = str1, str2 = " << str2 << std::endl;

    if (str1 == str2) {
        std::cout << "str1 is equal to str2" << std::endl;
    }
    else {
        std::cout << "str1 is not equal to str2" << std::endl;
    }

    if (str1 == "hello") {
        std::cout << "str1 is equal to \"hello\"" << std::endl;
    }
    else {
        std::cout << "str1 is not equal to \"hello\"" << std::endl;
    }

    return 0;
}