c++ code to search pattern in file

/******************************************************* * File : searchPattern.cpp * Author : saurabh gupta * Description : c++ code to search pattern in file * Source : http://www.ccplusplus.com/p/c_15.html * Date : Wednesday 29th Feb 2012 * ToDo : change the code for stream search ********************************************************/ #include <iostream> #include <fstream> #include <string> #include <vector> using namespace std; typedef std :: vector<int> vecInt; class CSearchString { private: vecInt m_vShifts; void m_computeShifts(const std::string &strPattern); public: int m_findFirst(const std::string &text, const std::string &strPattern); vecInt m_findAll(const std::string &text, const std::string &strPattern); }; // create the shift-lookup-table void CSearchString::m_computeShifts(const std::string &strPattern) { int nNextShift = 0; m_vShifts.clear(); m_vShifts.push_back(0); // shift to the first character // start with the second character, since the shift to the first is always 0 for(int i = 1; i < strPattern.length(); i++) { while(nNextShift > 0 && strPattern[nNextShift] != strPattern[i]) { nNextShift = m_vShifts[nNextShift]; } if(strPattern[nNextShift] == strPattern[i]) { nNextShift++; } m_vShifts.push_back(nNextShift); } } // search the string and return when the first occurrence is found int CSearchString::m_findFirst(const std::string &text, const std::string &strPattern) { int nNextShift = 0; m_computeShifts(strPattern); for(int i = 0; i < text.length(); i++) { while(nNextShift > 0 && strPattern[nNextShift] != text[i]) { nNextShift = m_vShifts[nNextShift - 1]; } if(strPattern[nNextShift] == text[i]) { nNextShift++; } if(nNextShift == strPattern.length()) { return i - (strPattern.length() - 1); // found the first so return } } return -1; } // search the string and put every occurence in a vector vecInt CSearchString::m_findAll(const std::string &text, const std::string &strPattern) { int nNextShift = 0; vecInt vPositions; m_computeShifts(strPattern); for(int i = 0; i < text.length(); i++) { while(nNextShift > 0 && strPattern[nNextShift] != text[i]) { nNextShift = m_vShifts[nNextShift - 1]; } if(strPattern[nNextShift] == text[i]) { nNextShift++; } if(nNextShift == strPattern.length()) { vPositions.push_back(i - (strPattern.length() - 1)); // found one, put in list nNextShift = m_vShifts[nNextShift - 1]; // restart strPattern with last shift } } return vPositions; } int main(int argc, char **argv) { // main begins if(argc <= 2){ cout << "Usage: " << argv[0] << " filename searchpattern" << endl; return 0; } std::string strPattern = argv[2]; // read the file. Since the file is read like this all white-characters // are eaten, so a search including white-characters will fail... fstream fs; std::string text, temp; fs.open(argv[1], ios::in); while(!fs.eof()) { fs >> temp; text += temp; } fs.close(); // search the file CSearchString search; vecInt pos_list = search.m_findAll(text, strPattern); // print out result std::vector<int>::iterator it; cout << "Found " << pos_list.size() << " occurrences" << endl; for(it = pos_list.begin(); it != pos_list.end(); it++) { temp = text.substr(*it, strPattern.length()); cout << "Pos=" << *it << " == " << temp << endl; } return 0; } //main ends /* * * [sgupta@rhel6x64 cpp]$ c++ search-string-pattern.cpp -o search-string-pattern [sgupta@rhel6x64 cpp]$ ./search-string-pattern Usage: ./search-string-pattern filename searchpattern [sgupta@rhel6x64 cpp]$ ./search-string-pattern search-string-pattern.cpp occurrences Found 1 occurrences Pos=2699 == occurrences [sgupta@rhel6x64 cpp]$ */