Can redirection of screen output to file change the result of a C++ code?
- by Biga
I am having this very weird behaviour with a C++ code: It gives me different results when running with and without redirecting the screen output to a file (reproducible in cygwin and linux). I mean, if I get the same executable and run it like ./run or run it like ./run >out.log, I get different results!
I use std::cout to output to screen, all lines ending with endl; I use ifstream for the input file; I use ofstream for output, all lines ending with endl.
I am using g++ 4.
Any idea what is going on?
UPDATE: I have hard-coded the input data, so 'ifstream' is not used, and problem persists.
UPDATE 2: That's getting interesting. I have probed three variables that are computed initially, and that's what I get when using with and without redirecting the output to file
redirected to file: 0 -0.02 0
direct to screen: 0 -0.02 1.04083e-17
So there's a round-off difference in the code variables with and without redirecting the output!
Now, why redirecting would interefere with an internal computation of the code?
UPDATE 3: If I redirect to /dev/null, I get the sam behaviour as outputing direct to screen, instead of redirecting to file.
