57 lines
1.4 KiB
C
57 lines
1.4 KiB
C
/* This file is part of the sample code and exercises
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* used by the class "Advanced Programming in the UNIX
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* Environment" taught by Jan Schaumann
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* <jschauma@netmeister.org> at Stevens Institute of
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* Technology.
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*
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* This file is in the public domain.
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*
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* You don't have to, but if you feel like
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* acknowledging where you got this code, you may
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* reference me by name, email address, or point
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* people to the course website:
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* https://stevens.netmeister.org/631/
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*/
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/*
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* This program illustrates that you an close the default
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* standard I/O filedescriptors. To reopen, you then need
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* to explicitly open the terminal device and dup(2) the
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* descriptor onto it.
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*/
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#include <err.h>
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#include <errno.h>
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#include <fcntl.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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int
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main() {
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int fd;
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if ((fd = open("/dev/tty", O_WRONLY)) < 0) {
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err(EXIT_FAILURE, "Unable to open /dev/tty");
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/* NOTREACHED */
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}
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(void)printf("Opened /dev/tty on fd#%d.\n", fd);
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(void)printf("Closing STDERR_FILENO...\n");
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(void)close(STDERR_FILENO);
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(void)fprintf(stderr, "This message will not be shown.\n");
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if (dup2(fd, STDERR_FILENO) < 0) {
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/* stderr is still closed */
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(void)fprintf(stdout, "Unable to dup2: %s\n", strerror(errno));
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exit(EXIT_FAILURE);
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/* NOTREACHED */
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}
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(void)fprintf(stderr, "Error messages back to normal.\n");
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(void)close(fd);
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return EXIT_SUCCESS;
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}
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