如何为程式码加上行号

         /*
         (C) OOMusou 2008 http://oomusou.cnblogs.com

         Filename    : map_code_line.cpp
         Compiler    : Visual C++ 9.0 / Visual Studio 2008
         Description : Demo how to add line number for code
         Release     : 07/18/2008 1.0
         */
         #include <iostream>
         #include <fstream>
         #include <string>
         #include <map>
         #include <algorithm>
         using namespace std;
         ifstream infile("map_code_line.cpp");
         ofstream outfile("map_code_line_r.cpp");
         struct print_map {
           void operator() (pair<int, string> p) {
             cout    << p.first << " " << p.second << endl;
             outfile << p.first << " " << p.second << endl;
           }
         };
         int main() {
           map<int, string> lines;
           string line;
           int line_num = 1;
           while(getline(infile, line))
           lines[line_num++] = line;
           infile.close();
           for_each(lines.begin(), lines.end(), print_map());
           outfile.close();
         }