字符串类的实现
#pragma once #include<iostream> using namespace std; class String { public: String(const char* str = ""); String(const String& other); String& operator=(const String& other); String& operator=(const char* str); char& operator[](unsigned int index); const char& operator[](unsigned int index) const; String& operator+=(const String& other); ~String(void); void Display() const; //允许 "aaa"+s friend String operator+(const String& s1, const String& s2); friend ostream& operator<<(ostream& os,const String& str); //istream第二个参数不能是const类型 friend istream& operator>>(istream& is, String& str); private: char* AllocAndCpy(const char* str); char* str_; }; #pragma warning(disable:4996)//屏蔽警告 #include "String.h" #include <string.h> String::String(const char* str) { str_ = AllocAndCpy(str); } String::String(const String& other) { str_ = AllocAndCpy(other.str_); } String& String::operator=(const String& other) { if (this == &other) return *this; delete[] str_; str_ = AllocAndCpy(other.str_); return *this; } char& String::operator[](unsigned int index) { //return str_[index]; //应该用non_const版本调用const版本。避免代码重复 //将*this对象转换为const对象,同时返回值还要去掉常量属性 return const_cast<char&>(static_cast<const String&>(*this)[index]); } const char& String::operator[](unsigned int index)const { return str_[index]; } String& String::operator=(const char* str) { delete[] str_; str_ = AllocAndCpy(str); return *this; } String::~String(void) { delete[] str_; } void String::Display() const { cout << str_ << endl; } char* String::AllocAndCpy(const char* str) { int len = strlen(str) + 1; char* newstr= new char[len]; memset(newstr,0,len); strcpy(newstr,str); return newstr; } //友元函数不是成员函数 String operator+(const String& s1, const String& s2) { //int len = strlen(s1.str_)+strlen(s2.str_)+1; //char *newstr = new char[len]; //memset(newstr,0,len); //strcpy(newstr,s1.str_); //strcat(newstr,s2.str_); //String tmp(newstr); //delete newstr;//防止内存泄漏 //return tmp; String str = s1; str += s2; return str; } ostream& operator<<(ostream& os, const String& str) { os << str.str_; return os; } //流运算符进行重载 istream& operator >> (istream& is, String& str) { char tmp[1024]; is >> tmp; str = tmp; return is; } String& String::operator+=(const String& other) { int len = strlen(str_) + strlen(other.str_) + 1; char* newchar = new char[len]; memset(newchar,0,len); strcpy(newchar, str_); strcat(newchar,other.str_); delete[] str_; str_ = newchar; return *this; } //继承 代码重用:组合和继承 //组合方式实现代码重用,通常将一个类作为另一个类的对象成员,委托给另一个对象实现 class A { public: void FunA() { ... } }; class B { public: void FunB() { ... a_.FunA(); ... } private: A a_;//组合一个A对象 };