fprintf problem (ofstream)

[Roberto Di Bernardo]

I wrote a program that creates a text file with some letters using ofstream.
Now I would like to format the text so that the letters are written in groups
of 5 and the rows are all the same length( i.e. DANIWEBFORUM becomes DANIW
EBFOR UM). To do this the fprintf function seemed the most appropriate. in the
following example I use integers, but it is just an example.

#include <string>
#include <iomanip>
#include <fstream>
#include <cstdio>

using namespace std;

int main()
{
    ofstream f;

    f.open("testo.txt");

    for(int i = 0; i < 21; i++)
    {
            f << i;  
            }

    f.close(); //to simulate file already created

    FILE *file;
    int number;
    file = fopen("testo.txt", "r+");
    if (file==NULL) perror ("Error opening file");
    else
    {
        do {
           number = fgetc (file);
           fprintf(file, "%-5.5i", number);
        } while (number != EOF);
     }
     fclose(file);
     return 0;
}

can this method work? or there is some function that I can use directly when
creating the file with ofstream?
please help

[Jim Pattee]

Your method will work. But you cannot format the output the way you want it
with the fprintf.
You are reading one character at a time. Print 5 characters then print a
space.
To force a line feed print the linefeed character "\n".
Your format string should be just an "i". What you have now, "%-5.5i", will
print a single number of 5 digits and 5 decimal places.