面试常常用到string类的实现,自己总结了一下:
#pragma once #include <iostream> #include <cassert> #include <iomanip> using namespace std; class string{ friend ostream& operator <<(ostream&,string&); friend istream& operator >>(istream&,string&); public: string(const char* str = NULL); //assignment constructor string(const string& str); ~string(){ delete [] m_data; } //get the length of string int size(){ return mystrlen(m_data); } //return substring 这里存在一些问题待改善 //当字符串的长度稍大一些时会出错; string substr(int pos); string substr(int pos,int len); //overload operator = string& operator =(const string& other); //overload operator + string operator +(const string& other)const; //overload operator += string& operator +=(const string& other); //overload operator == bool operator ==(const string& other)const; //overload operator [] char& operator [](unsigned int); private: char* m_data; };
cpp
#include "string.h" string::string(const char* str /* = NULL */) { if (!str) { m_data = new char[1]; *m_data = '\0'; } else { int nLen = strlen(str); m_data = new char[nLen + 1]; strcpy(m_data,str); } } string::string(const string& str) { m_data = new char[strlen(str.m_data)+1]; strcpy(m_data,str.m_data); } ostream& operator <<(ostream& oscout,string& str) { oscout<<str.m_data; return oscout; } istream& operator >>(istream& iscin,string& str) { char temp[255]; iscin>>setw(255)>>temp; str = temp; return iscin; } string string::substr(int pos) { /* int nLen = strlen(m_data); char* res = new char(nLen - pos +1); char* src = m_data + pos; strncpy(res,src,nLen-pos); string strres(res); return strres; */ int nLen = strlen(m_data); if (nLen < pos) { pos = nLen; } int nCopyLen = nLen - pos; char* res = new char(nLen - pos +1); char* dest = res; char* src = m_data + pos; for (int i = 0;i < nCopyLen; i++) { *dest++ = *src++; } *dest = '\0'; string strres(res); return strres; } string string::substr(int pos,int len) { int maxlen = strlen(m_data)-pos; if (maxlen < 0) maxlen = 0; int newLen = maxlen < len ? maxlen : len; char* res = new char(newLen+1); char* src = m_data + pos; strncpy(res,src,newLen); *(res+newLen) = '\0'; string strres(res); return strres; } string string::operator +(const string& other)const { string newString; if(!other.m_data) newString = *this; else if(!m_data) newString = other; else { newString.m_data = new char[strlen(m_data)+strlen(other.m_data)+1]; strcpy(newString.m_data,m_data); strcat(newString.m_data,other.m_data); } return newString; } string& string::operator =(const string& other) { if (this==&other) return *this; delete [] m_data; m_data = new char[strlen(other.m_data)+1]; strcpy(m_data,other.m_data); return *this; } string& string::operator +=(const string& other) { char* data = new char[strlen(m_data)+strlen(other.m_data)+1]; strcpy(data,m_data); delete [] m_data; m_data = data; strcat(m_data,other.m_data); return *this; } //overload operator == bool string::operator ==(const string& other)const { if ( strlen(other.m_data) != strlen(m_data) ) return false; return strcmp(m_data,other.m_data)?false:true; } //overload operator [] char& string::operator [](unsigned int index) { if (index >= 0 && index <= strlen(m_data)) return m_data[index]; return m_data[strlen(m_data)+1]; }
另外转置输出string例子
#include <iostream> #include <string> using namespace std; //只限英文字符 void ReverseString(string& str) { int nLen = str.size(); for (int i = 0; i < nLen/2; i++) { char cTmp = str[nLen-i-1]; str[nLen-i-1] = str[i]; str[i] = cTmp; } } //中英字符 void ReverseString1(string& str) { int nLen = str.size(); string strTmp; strTmp.resize(nLen,' '); for (int i =0; i < nLen; i++) { if ( str[i] < 255 && str[i] > 0) { strTmp[nLen-i-1] = str[i]; } else { strTmp[nLen-i-2] = str[i]; strTmp[nLen-i-1] = str[i+1]; ++i; } } str = strTmp; } int main(int argc, char* argv[]) { int nflag = 1; while (nflag) { cout<<"enter a string including both lowercase and upercase letters!"<<endl; string str; cin.clear(); cin.sync(); getline(cin,str); ReverseString1(str); cout<<str<<endl; cout<<"enter 0 to exit or 1 to continue"<<endl; cin>>nflag; } return 0; }