Thanks for the response and the link. As far as I can tell, I'm doing it right, but I still get the same result: the error message and no output file. Here's my updated code. As you can see from lines 16 and 17, I tried using both "ios" and "fstream" in front of "in" and "out". Neither worked. I didn't get the message "badbit is set" in line 24, so that means that it must be the failbit, right?

C++ Syntax (Toggle Plain Text)

// This program creates an output file that will be read by another
// program while this program is still writing to the output file.
 
#include "windows.h"
#include <fstream>
#include <iostream>
using namespace std;
 
int main ()
{
	fstream outs;
	cout << "Going to sleep\n";
	Sleep (5000);
	cout << "Waking up: Opening log file\n";
 
//	outs.open("DummyLogFile.txt", ios::in|ios::out);
	outs.open("DummyLogFile.txt", fstream::in|fstream::out);	
	if (outs.fail())
	{
		cout << "Unsuccessful opening log file for output\n";
 
		if (outs.bad ())
		{
                      cout << "badbit is set\n";
                }
         }
	else
		cout << "Successful opening log file for output\n";
 
	for (int i = 1; i <= 10; i++)
	{
		cout << "Line " << i << ": Hello world\n";
		outs << "Line " << i << ": Hello world\n";
		Sleep (1000);
	}
	outs.close ();
	return 0;
}

// This program creates an output file that will be read by another // program while this program is still writing to the output file. #include "windows.h" #include <fstream> #include <iostream> using namespace std; int main () { fstream outs; cout << "Going to sleep\n"; Sleep (5000); cout << "Waking up: Opening log file\n"; // outs.open("DummyLogFile.txt", ios::in|ios::out); outs.open("DummyLogFile.txt", fstream::in|fstream::out); if (outs.fail()) { cout << "Unsuccessful opening log file for output\n"; if (outs.bad ()) { cout << "badbit is set\n"; } } else cout << "Successful opening log file for output\n"; for (int i = 1; i <= 10; i++) { cout << "Line " << i << ": Hello world\n"; outs << "Line " << i << ": Hello world\n"; Sleep (1000); } outs.close (); return 0; }

The various combinations of the flags and the corresponding meaning as below:

C++ Syntax (Toggle Plain Text)

ios_base Flags 	         Meaning 
in 	                        Reads (file must exist)
out 	                       Empties and writes (creates if necessary)
out | trunc 	            Empties and writes (creates if necessary)
out | app 	            Appends (creates if necessary)
in I out 	              Reads and writes; initial position is the start (file must exist)
in | out | trunc 	   Empties, reads, and writes (creates if necessary)

ios_base Flags Meaning in Reads (file must exist) out Empties and writes (creates if necessary) out | trunc Empties and writes (creates if necessary) out | app Appends (creates if necessary) in I out Reads and writes; initial position is the start (file must exist) in | out | trunc Empties, reads, and writes (creates if necessary)

In your program, you use fifth combination, so the file you try to open must exist.

for you purpose, I think use flag 'out' will be ok. or use ofstream without flag(the default flag for ofstream is 'out').