实现string类

1 char字符串以'/0'结尾，但是strlen()时它不占大小，cout时它也不会输出来

2 new出来的char[]大小一定要满足操作，否则操作越界，delete时出错

  new出来的指针移动了，delete也会出错

3 模板函数的声明和定义要放在同一个文件里，默认放在头文件

strings.h:

#pragma once#include<string>class strings{public:strings();strings(const char* s);strings(const strings & other);  //拷贝构造函数strings(int n, char c); //常见一个包含n个字符为c的对象strings(const char* s, int n);   //将字符串初始化为s的前n个字符，即使已经到了串尾template<class T>strings(const T ptr1, const T ptr2);//用一个数组内的两个指针构造对象int size();strings& operator=(const strings& other);strings operator+(const strings& other);bool operator==(const strings& other);char operator[] (int index);friend std::ostream& operator<<(std::ostream& out, const strings& str);virtual ~strings();private:char* date;int datelength;};template<class T>strings::strings(const T ptr1, const T ptr2){T temp = ptr1;int size = sizeof(*ptr1);datelength = strlen(ptr1) - strlen(ptr2);date = new char[datelength + 1];int i = 0;for (temp; temp<ptr2; temp += size){date[i++] = *temp;}date[datelength] = '\0';}

strings.cpp

#include "stdafx.h"#include "strings.h"#include<string>#include<iostream>strings::strings() //默认构造空字符串，'\0'不占长度{datelength = 0;date = new char[1];*date = '\0';}strings::strings(const char* s){if (!s)//如果s为nullptr，则会为其初始化为空字符串，即以'\0'结尾{datelength = 0;date = new char[1];*date = '\0';}else{datelength = strlen(s);date = new char[datelength+1];//最后空间放'\0'strcpy(date, s);}}strings::strings(const strings & other) //other字符串已经被初始化，因此不可能为nullptr，不需要判断为空{datelength = other.datelength;date = new char[datelength + 1];strcpy(date, other.date);}strings::strings(int n, char c){datelength = n;date = new char[datelength + 1];for (int i = 0; i < datelength; i++)date[i] = c;date[datelength] = '\0'; //不能是date[datelength+1]，否则越界，析构时出错}strings::strings(const char* s, int n){datelength = n;date = new char[datelength + 1];strncpy(date, s, n);date[datelength] = '\0';}strings& strings::operator=(const strings& other){if (this->date == other.date)return *this;delete[] date;datelength = other.datelength;date = new char[datelength + 1];strcpy(date, other.date);return *this;}strings strings::operator+(const strings& other){strings temp;datelength = this->datelength + other.datelength;temp.datelength = datelength; //大小别忘了更新，否则后面赋值的时候越界temp.date = new char[temp.datelength + 1];strcpy(temp.date, date);strcat(temp.date, other.date);//要保证目标字符串由足够空间return temp; //这里要注意，它返回的是临时对象，因此函数返回值不能为引用}bool strings::operator==(const strings& other){if (this->datelength != other.datelength)return false;elsereturn strcmp(this->date, other.date) ? false : true;}char strings::operator[] (int index){if (index >= 0 && index < this->datelength)return this->date[index];}std::ostream& operator<<(std::ostream& out, const strings&  str){out << str.date;return out;}strings::~strings(){if (this->date){delete []  this->date;this->date= nullptr;}}

main函数：

// String.cpp : 定义控制台应用程序的入口点。//#include "stdafx.h"#include"strings.h"#include<iostream>#include<cstdlib>using namespace std;int _tmain(int argc, _TCHAR* argv[]){strings a;cout << "默认构造函数： " << a << endl;strings b("zhang");cout << "字符串构造： " << b << endl;strings c(b);cout << "拷贝构造函数： " << c << endl;strings d(5, '6');cout << "构造由5个‘6’组成的对象： " << d << endl;char *str= "123456";strings e(str, 3);cout << "用字符串的前3个字符构造对象： " << e<< endl;a = b;cout << "赋值号重载：" << a << endl;bool result = (a == b);cout << "等于号重载：" << result << endl;a = a + b;cout << "加号重载：" << a << endl;cout << "大小："<<a.size() << endl;char* ss = "123456";strings bb(&ss[0], &ss[3]);cout << "用字符串的两个指针构造对象：" << bb << endl;system("pause");return 0;}