The following example illustrates how to use formatting functions and manipulators. It also shows how to define and use functions that have a stream as an argument.

//Reads all the numbers in the file rawdata.dat and writes the numbers
//to the screen and to the file neat.dat in a neatly formatted way.
#include <iostream>
#include <fstream>
#include <cstdlib>
#include <iomanip>
using namespace std;

void make_neat(ifstream& messy_file, ofstream& neat_file,
             int number_after_decimalpoint, int field_width);
//Precondition: The streams messy_file and neat_file have been connected
//to files using the function open.
//Postcondition: The numbers in the file connected to messy_file have
//been written to the screen and to the file connected to the stream
//neat_file. The numbers are written one per line, in fixed point notation
//(i.e., not in e-notation), with number_after_decimalpoint digits after the
//decimal point; each number is preceded by a plus or minus sign and
//each number is in a field of width field_width. (This function does not
//close the file.)

int main( )
{
     ifstream fin;
     ofstream fout;

     fin.open("rawdata.dat");
     if (fin.fail( ))
         {
             cout << "Input file opening failed.\n";
             exit(1);
         }

     fout.open("neat.dat");
     if (fout.fail( ))
         {
             cout << "Output file opening failed.\n";
             fin.close( );
             exit(1);
         }

     make_neat(fin, fout, 5, 12);

     fin.close( );
     fout.close( );

     cout << "End of program.\n";
     return 0;
}

//Uses iostream, fstream, and iomanip.
void make_neat(ifstream& messy_file, ofstream& neat_file,
         int number_after_decimalpoint, int field_width)
{
     double next;
     neat_file.setf(ios::fixed);
     neat_file.setf(ios::showpoint);
     neat_file.setf(ios::showpos);
     neat_file.precision(number_after_decimalpoint);
     cout.setf(ios::fixed);
     cout.setf(ios::showpoint);
     cout.setf(ios::showpos);
     cout.precision(number_after_decimalpoint);

     while (messy_file >> next)
         {
             cout << setw(field_width) << next << endl;
             neat_file << setw(field_width) << next << endl;
         }
}