一、头文件

#pragma once
#include <iostream>/*** 自定义String类*/
class String 
{
public:String();String(const char *pstr);String(const String &str);~String();String &operator= (const String &str);String &operator= (const char *pstr);String &operator+= (const String &str);String &operator+= (const char *pstr);char &operator[] (std::size_t index);const char &operator[] (std::size_t index) const;std::size_t size() const;const char* c_str() const;friend bool operator== (const String &leftStr, const String &rightStr);friend bool operator!= (const String &leftStr, const String &rightStr);friend bool operator< (const String &leftStr, const String &rightStr);friend bool operator> (const String &leftStr, const String &rightStr);friend bool operator<= (const String &leftStr, const String &rightStr);friend bool operator>= (const String &leftStr, const String &rightStr);friend std::ostream &operator<< (std::ostream &os, const String &str);friend std::istream &operator>> (std::istream &is, String &str);private:char * _pstr;
};String operator+(const String &thisStr, const String &otherStr);
String operator+(const String &thisStr, const char *otherpStr);
String operator+(const char *thisPstr, const String &otherStr);

二、String实现

#include <cstring>
#include "08_MyString.hh"using namespace std;/*** 无参构造函数
*/
String::String()
: _pstr(new char[1]{0}) 
{strcpy(_pstr, "");	
}/*** 有参构造函数
*/
String::String(const char *pstr) 
: _pstr(new char[strlen(pstr) + 1]{0})
{strcpy(_pstr, pstr);
}/*** 拷贝构造函数
*/
String::String(const String &str)
: _pstr(new char[strlen(str._pstr) + 1]{0})
{strcpy(_pstr, str._pstr);
}/*** 析构函数
*/
String::~String() {delete [] _pstr;
}/*** 重载赋值运算符函数
*/
String &String::operator=(const String &str) {if (this != &str) { // 跳过自赋值delete [] _pstr;_pstr = new char[strlen(str._pstr) + 1]{0};strcpy(_pstr, str._pstr);} return *this; 
}
String &String::operator=(const char *pstr) {delete [] _pstr;_pstr = new char[strlen(pstr) + 1]{0};strcpy(_pstr, pstr);return *this;
}/*** 重载+=
*/
String &String::operator+= (const String &str) {size_t newLen = strlen(_pstr) + strlen(str._pstr) + 1;char *newStr = new char[newLen]{0};strcat(newStr, _pstr);strcat(newStr, str._pstr);delete [] _pstr;_pstr = newStr;return *this;
}
String &String::operator+= (const char *pstr) {size_t newLen = strlen(_pstr) + strlen(pstr) + 1;char *newStr = new char[newLen]{0};strcat(newStr, _pstr);strcat(newStr, pstr);delete [] _pstr;_pstr = newStr;return *this;
}/*** 重载下标运算符
*/
char &String::operator[] (size_t index) {if (index < strlen(_pstr)) { // 未越界return _pstr[index];}else {static char nullchar = '\0';return nullchar;}	
}
const char &String::operator[] (size_t index) const {if (index < strlen(_pstr)) { // 未越界return _pstr[index];}else {static char nullchar = '\0';return nullchar;}	
}/*** 获取字符串长度
*/
size_t String::size() const {return strlen(_pstr);
}/*** 返回C风格字符串
*/
const char *String::c_str() const {return _pstr;
}/*** 重载==
*/
bool operator==(const String &leftStr, const String &rightStr) {return strcmp(leftStr._pstr, rightStr._pstr) == 0 ? true : false;
}
/*** 重载!=
*/
bool operator!=(const String &leftStr, const String &rightStr) {return strcmp(leftStr._pstr, rightStr._pstr) != 0 ? true : false;
}
/*** 重载<
*/
bool operator<(const String &leftStr, const String &rightStr) {return strcmp(leftStr._pstr, rightStr._pstr) < 0 ? true : false;
}
/*** 重载>
*/
bool operator>(const String &leftStr, const String &rightStr) {return strcmp(leftStr._pstr, rightStr._pstr) > 0 ? true : false;
}
/*** 重载<=
*/
bool operator<=(const String &leftStr, const String &rightStr) {int res = strcmp(leftStr._pstr, rightStr._pstr); return res > 0 ? false : true;
}
/*** 重载>=
*/
bool operator>=(const String &leftStr, const String &rightStr) {int res = strcmp(leftStr._pstr, rightStr._pstr); return res < 0 ? false : true;
}/*** 重载输出流函数
*/
ostream &operator<< (ostream &os, const String &str) {os << str._pstr;return os;
}/*** 重载输入流函数
*/
istream &operator>> (istream &is, String &str) {char buf[4096];is.getline(buf, sizeof(buf));delete [] str._pstr;str._pstr = new char[strlen(buf) + 1];strcpy(str._pstr, buf);return is;
}/*** 重载+
*/
String operator+(const String &thisStr, const String &otherStr) {String temp(thisStr.c_str());temp+=otherStr.c_str();return temp;
}
String operator+(const String &thisStr, const char *otherPstr) {String temp(thisStr.c_str());temp+=otherPstr;return temp;
}
String operator+(const char *thisPstr, const String &otherStr) {String temp(thisPstr);temp+=otherStr.c_str();return temp;
}