Question

very simple program, not sure why it isn’t working:

#include <iostream>
#include <fstream>
#include <stdio.h>

using namespace std;

int main ()

{
ofstream myfile ("test.txt");
if (myfile.is_open()) 
{
    for(  int i = 1;  i < 65535;  i++  )

     {
     myfile << ( "<connection> remote 208.211.39.160 %d udp </connection>\n", i );
     }
    myfile.close();
}
  return 0;
}

Basically it should print that sentence 65535 times, and then save it to a txt file. But the txt file just has a list of numbers from 1 to 65535, no words or formatting. Any ideas? Thanks for help.

Answer 1

If you want to concatenate the output, just pipe your data into two << operators, as such:

myfile << "<connection> remote 208.211.39.160 %d udp </connection>\n" << i;

Note that interpolation does not work in that case, so if you want to put your i variable into the middle of the string, you have to either split it by hand:

myfile << "<connection> remote 208.211.39.160 " << i << " udp </connection>\n"

Or apply some sort of other interpolation formatting before outputting it.

The problem

The problem exists in your code because in C++, (a, b) (the comma operator) returns b. So, in your code it meant you just wrote i to a file.