pongo庞果：xml字符串文件的解析——为什么我的代码效率低？

最近正在学习C++ STL，尝试着使用C++解庞果上面的在线编程挑战题目，结果总是说超过3s时间。这是为啥呀为啥呀？哥只是用了个string 而已啊

题目 ：http://hero.pongo.cn/Home/Index  蓝港在线：xml字符串文件的解析

代码贴出来，留待日后有能力了改进效率：

#include <iostream>#include <sstream>#include <string>#include <boost/progress.hpp>using namespace std;using namespace boost;string intToString(const int n ){   std::stringstream newstr;   newstr << n;   return newstr.str();}void ltrim(string& s){   const char drop = ' ';   // trim right   s.erase(s.find_last_not_of(drop)+1);   // trim left   //s.erase(0,s.find_first_not_of(drop));}// LAB means Left Angle Brace: "<"void jumpTilEndorLAB(string& str, int& pos){   while((str[pos] != '\0') && (str[pos] != '<'))   {      pos++;   }}//parse xml header: <?xml .... ?>void parseXmlHeader(string& str, int& pos){   if(('<' == str[pos]) && ('?' == str[pos+1]))   {      while(('?' != str[pos]) && ('>' != str[pos+1]))      {         pos++;      }      pos += 2;   //jump over ?>      jumpTilEndorLAB(str, pos);   }   return ;}// parse the xmlstring ParsingXML(string str){   string   result;   result.reserve(1024);   int bodyPos = 0;   int length = str.length();    parseXmlHeader(str, bodyPos);   if(bodyPos == length)   {      return result;   }   // Body format:   //<catigory1_name>   //    <entity1_name>   //          <attr1="..." att2="..." />   //    </entity1_name>   //    <entity2...>   //</catigory1_name>   int categoryStart = bodyPos;   int categoryEndAll = length;   // parse all categories   while( categoryStart != categoryEndAll)   {      string category(str.substr(categoryStart+1, str.find_first_of('>', categoryStart)-categoryStart-1));      //cout << category << endl;      result += (category + "\r\n");      int entityStart = categoryStart + category.length() + 2; //jump over <category_name>      int entityEndAll = str.find(("</"+category+">"), categoryStart);      jumpTilEndorLAB(str, entityStart);      //parse the category's entities      int entityIndex = 1;      while(entityStart != entityEndAll)      {         string entity(str.substr(entityStart+1, str.find_first_of('>', entityStart)-entityStart-1));         //cout << "\t" << entity << " " << entityIndex++ << endl;         result += "\t";         result += (entity + " " + intToString(entityIndex) + "\r\n");         entityIndex++;         int attrStart = entityStart + 2 + entity.length();  //jump over <entity_name>         while(str[attrStart] != '<')          {            attrStart++;         }         attrStart++;   //jump over the "<" before attribute         while((str[attrStart] == ' ') || (str[attrStart] == '\t') ||             (str[attrStart] == '\r') || (str[attrStart] == '\n'))   // jump over ' ' before attribute if spaces exist         {            attrStart++;         }         // parse the attributes         while((str[attrStart] != '/') && (str[attrStart+1] != '>'))         {            int equivalentPos = str.find_first_of('=', attrStart);            string attrName = str.substr(attrStart, equivalentPos-attrStart);            ltrim(attrName);            //cout << "\t\t" << attrName << ":";            result += "\t\t";            result += (attrName + ":");            int valueBegin = str.find_first_of('\"', equivalentPos+1)+1;            int valueEnd = str.find_first_of('\"', valueBegin+1);            string attrValue = str.substr(valueBegin, valueEnd-valueBegin);            //cout << attrValue << endl;            result += (attrValue + "\r\n");            attrStart = valueEnd + 1;  //parse next attribute            while((str[attrStart] == ' ') || (str[attrStart] == '\t') ||                (str[attrStart] == '\r') || (str[attrStart] == '\n'))   // jump over ' ' before attribute if spaces exist            {               attrStart++;            }         }         entityStart = attrStart + 5 + entity.length();   //jump over "/></entity_name>"         jumpTilEndorLAB(str, entityStart);   //parse next entity      }      categoryStart = entityStart + 3 + category.length();   //jump over </category_name>      jumpTilEndorLAB(str, categoryStart);         //parse next category   }   return result;}int main(){      string str1("<?xml version=\"1.0\" ?>\\r\n<Books>\\r\n\t<Book>\\r\n\t\t<Name = \"The C++ Programming Language\" \\r\n\t\tAuthor=\"Bjarne Stroustrup\" />\\r\n\t</Book>\r\n\t<Book>\\r\n\t\t<Name = \"Effective C++\" \\r\n\t\tAuthor = \"Scott Meyers\" />\\r\n\t</Book>\\r\n</Books>");   //cout << str1 << endl;   string result1;   {      progress_timer pt;      for(int i = 0; i < 1000; i++)      {         result1 = ParsingXML(str1);      }   }   cout << result1;   return 1;} 

注：此代码效率低，需要改进！