How To Redirect Output To Dev Null In C
Basically, you're ripping the floor out from under your program without guaranteeing that the Right Thing has happened to put a new floor back. The 'stdout' file pointer will continue to work, but anything not informed of the change might not -- like cout, and any subprocesses you happen to run. Their output may not go where you expected, or go nowhere at all, or crash. It might work right, if the next file opened happens to land at file descriptor 1 -- or it might not. The behavior is undefined and at the mercy of what libraries and compiler you're using. All that's guaranteed after you do that is that stdio routines like printf() will go where you redirected.
Whatever file descriptor 1 went to before, might not be properly closed after freopen, either. If stdout was an open file descriptor to a terminal preventing your ssh window from closing, such is life.
The 'right thing' to do if you really want to redirect 'standard output', not just the stdio external variable 'stdout', is to ensure that the file you want is opened specifically as file descriptor one, which is what dup2() does in the example you were given. Which is much simpler than it looks once you realize it's redirecting twice: Once for stdout, once for stderr. Re-opening onto file descriptor one with dup2() also guarantees that whatever was there before, is forced to close. This could be especially important if that happened to be a terminal or device file.
Also, your example is concerning. Never mix printf and cout, for starters, especially if you're going to play funny games with redirection.
How To Redirect Output To Dev Null In C Pdf
How To Redirect Output To Dev Null In Code
/path/to/program arg1 arg2 /dev/null 2 /dev/null The syntax 2&1 means 'Send output currently going to file descriptor 2 to the same place that output going to file descriptor 1 is going to'. is omitting the default of FD1, so it is semantically the same as 1, which might make 2 make more sense. Another way to do it: $ command &/dev/null. Or you can close stdout and stderr for the command being executed: $ command 1&- 2&. Remember to add an additional & at the end of the statement to run the command in the background. Thank you Giuseppe for the tip. Input and output redirection in the C shell. Before the C shell executes a command, it scans the command line for redirection characters. Note that the default standard input for a command run detached is not changed to the empty /dev/null file. Instead, the standard input remains the original standard input of the shell. I also use the /dev/null redirection to suppress an output from SQLPLUS to the stdout. But now I want to execute another SQLPLUS statement (in the same script file) and I need to send that new output to STDOUT so it could be displayed to the user. All data written on a /dev/null or /dev/zero special file is discarded by the system. /cakewalk-vst-adapter-download-crack.html. Use /dev/null to send any unwanted output from program/command and syntax is: command /dev/null. This syntax redirects the command standard output messages to /dev/null where it is ignored by the shell. OR command 2/dev/null. Jun 05, 2014 What is a null (/dev/null) file in a Linux or Unix-like systems? /dev/null is nothing but a special file that discards all data written to it. The length of the null device is always zero. In this example, first, send output of date command to the screen and later to the /dev/null i.e. Discards date command output. What does 2/dev/null mean? The operator redirects the output usually to a file but it. Browse other questions tagged command-line bash redirect stdout.