-/* Close standard output, exiting with status 'exit_failure' on failure.
- If a program writes *anything* to stdout, that program should `fflush'
- stdout and make sure that it succeeds before exiting. Otherwise,
- suppose that you go to the extreme of checking the return status
- of every function that does an explicit write to stdout. The last
- printf can succeed in writing to the internal stream buffer, and yet
- the fclose(stdout) could still fail (due e.g., to a disk full error)
- when it tries to write out that buffered data. Thus, you would be
- left with an incomplete output file and the offending program would
- exit successfully.
-
- FIXME: note the fflush suggested above is implicit in the fclose
- we actually do below. Consider doing only the fflush and/or using
- setvbuf to inhibit buffering.
-
- Besides, it's wasteful to check the return value from every call
- that writes to stdout -- just let the internal stream state record
- the failure. That's what the ferror test is checking below.
+/* Close standard output. On error, issue a diagnostic and _exit
+ with status 'exit_failure'.
+
+ Also close standard error. On error, _exit with status 'exit_failure'.
+
+ Since close_stdout is commonly registered via 'atexit', POSIX
+ and the C standard both say that it should not call 'exit',
+ because the behavior is undefined if 'exit' is called more than
+ once. So it calls '_exit' instead of 'exit'. If close_stdout
+ is registered via atexit before other functions are registered,
+ the other functions can act before this _exit is invoked.
+
+ Applications that use close_stdout should flush any streams
+ other than stdout and stderr before exiting, since the call to
+ _exit will bypass other buffer flushing. Applications should
+ be flushing and closing other streams anyway, to check for I/O
+ errors. Also, applications should not use tmpfile, since _exit
+ can bypass the removal of these files.