模拟实现String类(1)_深拷贝

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"test.cpp"

#define _CRT_SECURE_NO_WARNINGS 1#include <iostream>using namespace std;#include "Sring.h"void Test1(){String str1("hello");cout<<str1<<endl;String str2("haha");cout<<str2<<endl;String str3(str1);cout<<str3<<endl;}void Test2(){String str1("hello");cout<<str1<<endl;String str2;str2 = str1;cout<<str2<<endl;}void Test3(){String str1("hallo");cout<<str1<<endl;cout<<strlen(str1.c_str())<<endl;str1[1] = 'e';cout<<str1<<endl;}void Test4(){String str1("hello");str1.PushBack('a');cout<<str1<<endl;String str2("hello");str2.PushBack(" world");cout<<str2<<endl;cout<<str2.Size()<<endl;cout<<str2.Capacity()<<endl;}void Test5(){String s1("hello");String s2("who");s1.Insert(3,s2);cout<<s1<<endl;cout<<s1.Size()<<endl;String s3("abcdefghi");s3.Erase(2,3);cout<<s3<<endl;cout<<s3.Size()<<endl;}int main(){//Test1();//Test2();//Test3();//Test4();Test5();system("pause");return 0;}

"String.h"

#pragma once#include <assert.h>#include <string>class String{friend ostream& operator<<(ostream& os,String& str);public://构造函数String(const char* str = "")//缺省给一个空字符串，使求长度的时候，不会出现错误:_size(strlen(str)),_capacity(strlen(str)+1)//容量多加一个是放'\0',_str(new char[_capacity]){strcpy(_str,str);}//析构函数~String(){if (_str){delete[] _str;_str = NULL;_size = 0;_capacity = 0;}}//拷贝构造函数String(const String& s):_size(s._size),_capacity(s._capacity),_str(new char[_capacity]){//深拷贝，给_str一块自己的空间，使两个指针分别指向两个不同的空间strcpy(_str,s._str);}////传统写法//String& operator=(const String& s)//{////防止自身给自身赋值//if (this != &str)//{//delete[] _str;//_str = new char[strlen(s._str)+1];//strcpy(_str,s._str);////错误示范////刚开始最后一句写成了_str = s._str////造成了浅拷贝的错误////同一块空间被释放两次导致程序错误//}//return *this;//}//现代写法，强盗式逻辑String& operator=(String s){swap(_size,s._size);swap(_capacity,s._capacity);swap(_str,s._str);return *this;}char* c_str(){return _str;}char& operator[](int index){return _str[index];}void PushBack(char ch){CheckCapacity(1);//_str[_size] = ch;//_size++;//_str[_size] = '\0';_str[_size++] = ch;_str[_size] = '\0';//最后一个字符一定要记得放入一个'\0'}void PushBack(char* str){CheckCapacity(strlen(str));char* tmp1 = _str;while (*tmp1){tmp1++;}char* tmp2 = str;while (*tmp2){*tmp1++ = *tmp2++;}*tmp1 = '\0';_size += strlen(str);}size_t Size(){return _size;}size_t Capacity(){return _capacity;}bool Empty(){if (_str){return false;} else{return true;}}String& Insert(size_t pos, const String& s){CheckCapacity(strlen(s._str));int size1 = _size;int newsize1 = _size;int size2 = s._size;int newsize2 = s._size;int count = size2;//while (size2--)//{//_str[size1-1+count] = _str[size1-1];//size1--;//}for (int i = size1-1;i >= pos;i--){_str[i+count] = _str[i];}char* tmp = s._str;while (count--){_str[pos++] = *tmp++;}_size = newsize1+newsize2;_str[_size] = '\0';return *this;}String& Erase(size_t pos,size_t len){int newlen = strlen(_str);assert((pos >= 0) && (pos < newlen));assert((len > 0) && (len <= newlen));int size = strlen(_str) - len;int count = len;for (int i = pos;i < newlen;i++){_str[i] = _str[i + len];}_str[size] = '\0';_size -= count;return *this;}protected:void CheckCapacity(int count){if ((_size+count) >= _capacity){int _newcapacity = (_size+count)>(2*_capacity)?(_size+count):(2*_capacity);_capacity = _newcapacity;char* tmp = new char[_newcapacity];strcpy(tmp,_str);delete[] _str;_str = tmp;}}private:size_t _size;size_t _capacity;char* _str;};ostream& operator<<(ostream& os,String& str){os<<str._str;return os;}

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