How To Redirect Output To Dev Null In C
admin 15.04.2020
freopen DOES NOT redirect standard output! You are only redirecting the C file pointer 'stdout', not the file descriptor it uses.
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.
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.
- 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.
- Redirection operators are evaluated left-to-right. You wrongly put 2&1 first, which points 2 to the same place, as 1 currently is pointed to which is the local terminal screen, because you have not redirected 1 yet. You need to do either of the following: 2/dev/null 1/dev/null google-chrome & Or. 2/dev/null 1&2 google-chrome &.
How To Redirect Output To Dev Null In C 1
How To Redirect Output To Dev Null In C R
Uvi workstation vst free download. All data written on a /dev/null or /dev/zero special file is discarded by the system. 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.
Error code 80073712 windows 7. Mar 13, 2019 Here is the roundup about how to solve the failed to flash in 3uTools. Feb 28, 2019 Many users were met various error codes when they flashing their iDevice in iTunes or 3uTools, here 3uTools summarizes some common error codes for you(some with.