How to read groups of integers from a file, line by line in C++

Question

I have a text file with on every line one or more integers, seperated by a space. How can I in an elegant way read this with C++? If I would not care about the lines I could use cin >>, but it matters on which line integers are.

Example input:

1213 153 15 155
84 866 89 48
12
12 12 58
12

Answer 1

It depends on whether you want to do it in a line by line basis or as a full set. For the whole file into a vector of integers:

int main() {
   std::vector<int> v( std::istream_iterator<int>(std::cin), 
                       std::istream_iterator<int>() );
}

If you want to deal in a line per line basis:

int main()
{
   std::string line;
   std::vector< std::vector<int> > all_integers;
   while ( getline( std::cin, line ) ) {
      std::istringstream is( line );
      all_integers.push_back( 
            std::vector<int>( std::istream_iterator<int>(is),
                              std::istream_iterator<int>() ) );
   }
}

Answer 2

You could do smtng like this(I used cin, but you can use any other file stream):

string line;
while( getline( cin, line ) )
{
 istringstream iss( line );
 int number;
 while( iss >> number )
  do_smtng_with_number();
}

Or:

int number;
while( cin >> number )
{
 do_smtng_with_number();
}