73 lines
1.7 KiB
C
73 lines
1.7 KiB
C
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/* 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 trivial program illustrates how we might normally read and write
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* to a simple file. Here, we simply open the source code file, read the
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* first few bytes, then append a comment.
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*
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* What happens if we do not open with O_APPEND?
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*/
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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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#define BUFFSIZE 64
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#define COMMENT "\n/* Just another comment. */\n"
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#define SOURCE "./rwex.c"
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int
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main() {
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int fd, n;
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int len;
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char buf[BUFFSIZE];
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if ((fd = open(SOURCE, O_RDWR | O_APPEND)) == -1) {
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fprintf(stderr, "Unable to open '%s': %s\n",
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SOURCE, strerror(errno));
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exit(EXIT_FAILURE);
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}
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if ((n = read(fd, buf, BUFFSIZE)) > 0) {
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if (write(STDOUT_FILENO, buf, n) != n) {
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fprintf(stderr, "Unable to write: %s\n",
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strerror(errno));
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exit(EXIT_FAILURE);
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}
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} else if (n == -1) {
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fprintf(stderr, "Error reading from %s: %s\n",
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SOURCE, strerror(errno));
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exit(EXIT_FAILURE);
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}
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printf("\n\nOk, we read the first %d bytes. Now let's write something.\n", BUFFSIZE);
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len = sizeof(COMMENT) - 1;
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if (write(fd, COMMENT, len) != len) {
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fprintf(stderr, "Unable to write: %s\n",
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strerror(errno));
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exit(EXIT_FAILURE);
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}
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(void)close(fd);
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return EXIT_SUCCESS;
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}
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/* Just another comment. */
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