#include <string>
#include <sstream>
#include <iostream>

int main()
{
    // open the stream which contains the city data
    // (this example uses a stringstream instead of a filestream)
    std::istringstream stm( R"(
A|City1|Data.1|Data.2|Data.3
R|01R|Data.4|Data.5|Data.6
R|02R|Data.4|Data.5|Data.6
R|03R|Data.4|Data.5|Data.6
R|04R|Data.4|Data.5|Data.6

A|City2|Data..1|Data..2|Data..3
R|01R|Data..4|Data..5|Data..6
R|02R|Data..4|Data..5|Data..6
R|03R|Data..4|Data..5|Data..6
R|04R|Data..4|Data..5|Data..6

A|City3|Data...1|Data...2|Data...3
R|01R|Data...4|Data...5|Data...6
R|02R|Data...4|Data...5|Data...6
R|03R|Data...4|Data...5|Data...6
R|04R|Data...4|Data...5|Data...6

                          )" ) ;

   // get the city name
   std::string city_name = "City2" ;

   // we need to look a line starting with
   // the city_name prefixed by "A|" and suffixed by '|'
   const std::string search_string = "A|" + city_name + '|' ;

   // read and discard lines from the stream
   // till we get to a line starting with the search_string
   std::string line ;
   while( std::getline( stm, line ) && line.find(search_string) != 0 ) ;

   // check if we have found such a line, if not report an error
   if( line.find(search_string) != 0 )
   {
       std::cerr << "city '" << city_name << " was not found\n" ;
       return 1 ;
   }

   // we need to form a string that would include the whole set of data
   // based on the selection of City
   std::string result = line + '\n' ; // result initially contains the first line

   // now keep reading line by line till we get an empty line or eof
   while( std::getline( stm, line ) && !line.empty() )
      result += line + '\n' ; // append this line to the result

   // use the result (in this example, we just print it out)
   std::cout << "data for '" << city_name << "'\n--------------\n" << result ;
}