String& String::operator=(const char* c) { return operator=(String(c));//?????????? }

这段代码是字符串类的赋值运算符的实现，它的作用是将一个 C 风格的字符串（即以 '\0' 结尾的字符数组）赋值给字符串类的对象。具体来说，它的实现是将一个 C 风格的字符串转换成一个字符串类的对象，然后调用另一个重载版本的赋值运算符来完成赋值操作。

这里的重载版本的赋值运算符是 String& String::operator=(const String& str)，它接受一个字符串类的对象作为参数。因此，代码中的 operator=(String(c)) 的作用是将 C 风格的字符串 c 转换成一个字符串类的对象，并将该对象作为参数传递给另一个赋值运算符来完成赋值操作。

这里还需要注意的是，代码中的 operator=() 函数使用了递归调用的方式，这样可能会导致栈溢出的问题。因此，在实际编程中，需要注意这个问题，并采取相应的措施来避免栈溢出。

相关问题

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; };

以下是 String 类的实现以及在主函数 main() 中的测试。

#include <iostream>
#include <cstring>

using namespace std;

class String {
public:
    String(const char *str = NULL);
    String(const String& other);
    ~String(void);
    String& operator=(char *str);
    String& operator=(const String& other);
    int operator==(String& other);
    int operator==(char *str);
private:
    char *m_data;
    int length;
};

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

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

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

String& String::operator=(char *str) {
    if (m_data == str) {
        return *this;
    }
    if (str != NULL) {
        length = strlen(str);
        char *temp = new char[length + 1];
        strcpy(temp, str);
        delete[] m_data;
        m_data = temp;
    }
    else {
        length = 0;
        delete[] m_data;
        m_data = new char[1];
        *m_data = '\0';
    }
    return *this;
}

String& String::operator=(const String& other) {
    if (m_data == other.m_data) {
        return *this;
    }
    length = other.length;
    char *temp = new char[length + 1];
    strcpy(temp, other.m_data);
    delete[] m_data;
    m_data = temp;
    return *this;
}

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

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

int main() {
    String s1("hello");
    String s2(s1);
    String s3("world");
    String s4;
    s4 = s1;

    cout << s1.operator==("hello") << endl; // 1
    cout << s1.operator==(s2) << endl; // 1
    cout << s1.operator==(s3) << endl; // 0
    cout << s1.operator==(s4) << endl; // 1

    return 0;
}

填充下面这个程序中所有出现// TODO: fill the code这个任务的地方#include <iostream> #include <cstring> #include "ourstring.h" #include "strlib.h" using namespace std; OurString::OurString(){ // TODO: fill the code } OurString::OurString(const char *str){ // TODO: fill the code } OurString::OurString(const OurString &dstr){ // TODO: fill the code } OurString::~OurString(){ // TODO: fill the code } string OurString::toString() const{ // TODO: fill the code } OurString OurString::subStr(unsigned int start, unsigned int n) const{ // TODO: fill the code } bool OurString::operator > (const OurString &dstr) const{ // TODO: fill the code } bool OurString::operator < (const OurString &dstr) const{ // TODO: fill the code } bool OurString::operator == (const OurString &dstr) const{ // TODO: fill the code } unsigned int OurString::length () const{ // TODO: fill the code } const OurString& OurString::operator = (const OurString &dstr){ // TODO: fill the code } const OurString& OurString::operator = (const char *str){ // TODO: fill the code } char& OurString::operator[](int index){ // TODO: fill the code } const OurString OurString::operator + (const OurString &dstr) const{ // TODO: fill the code } const OurString OurString::operator + (const char *str) const{ // TODO: fill the code } const OurString& OurString::operator += (const OurString &dstr){ // TODO: fill the code } const OurString& OurString::operator += (const char *str){ // TODO: fill the code } ostream & operator<<(ostream &os, const OurString &dstr){ // TODO: fill the code } istream & operator>>(istream &is, OurString &dstr){ // TODO: fill the code }

好的，下面是填充后的代码，每个 TODO 已经被替换成相应的实现：

#include <iostream>
#include <cstring>
#include "ourstring.h"
#include "strlib.h"
using namespace std;

OurString::OurString(){
    str = new char[1];
    str[0] = '\0';
}

OurString::OurString(const char *str){
    this->str = new char[strlen(str)+1];
    strcpy(this->str, str);
}

OurString::OurString(const OurString &dstr){
    this->str = new char[dstr.length()+1];
    strcpy(this->str, dstr.str);
}

OurString::~OurString(){
    delete [] str;
}

string OurString::toString() const{
    return string(str);
}

OurString OurString::subStr(unsigned int start, unsigned int n) const{
    if (start >= length()) return OurString();
    n = (n > length() - start) ? length() - start : n;
    return OurString(str + start, str + start + n);
}

bool OurString::operator > (const OurString &dstr) const{
    return strcmp(str, dstr.str) > 0;
}

bool OurString::operator < (const OurString &dstr) const{
    return strcmp(str, dstr.str) < 0;
}

bool OurString::operator == (const OurString &dstr) const{
    return strcmp(str, dstr.str) == 0;
}

unsigned int OurString::length () const{
    return strlen(str);
}

const OurString& OurString::operator = (const OurString &dstr){
    if (this != &dstr) {
        delete [] str;
        str = new char[dstr.length()+1];
        strcpy(str, dstr.str);
    }
    return *this;
}

const OurString& OurString::operator = (const char *str){
    if (this->str != str) {
        delete [] this->str;
        this->str = new char[strlen(str)+1];
        strcpy(this->str, str);
    }
    return *this;
}

char& OurString::operator[](int index){
    return str[index];
}

const OurString OurString::operator + (const OurString &dstr) const{
    OurString s;
    s.str = new char[length() + dstr.length() + 1];
    strcpy(s.str, str);
    strcat(s.str, dstr.str);
    return s;
}

const OurString OurString::operator + (const char *str) const{
    OurString s;
    s.str = new char[length() + strlen(str) + 1];
    strcpy(s.str, this->str);
    strcat(s.str, str);
    return s;
}

const OurString& OurString::operator += (const OurString &dstr){
    *this = *this + dstr;
    return *this;
}

const OurString& OurString::operator += (const char *str){
    *this = *this + str;
    return *this;
}

ostream & operator<<(ostream &os, const OurString &dstr){
    os << dstr.str;
    return os;
}

istream & operator>>(istream &is, OurString &dstr){
    string s;
    is >> s;
    dstr = s.c_str();
    return is;
}