$ cat -n ostep/code/intro/io.c
1 #include <stdio.h>
2 #include <unistd.h>
3 #include <assert.h>
4 #include <fcntl.h>
5 #include <sys/stat.h>
6 #include <sys/types.h>
7 #include <string.h>
8
9 int main(int argc, char *argv[]) {
10 int fd = open("/tmp/file", O_WRONLY | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR);
11 assert(fd >= 0);
12 char buffer[20];
13 sprintf(buffer, "hello world\n");
14 int rc = write(fd, buffer, strlen(buffer));
15 assert(rc == (strlen(buffer)));
16 fsync(fd);
17 close(fd);
18 return 0;
19 }
$ ./io
$ cat /tmp/file
hello world
$ ls -ld /tmp
drwxrwxrwt 19 root root 12288 Jun 5 11:43 /tmp
$ ls -l /tmp/file
-rw------- 1 perry perry 12 Jun 5 11:43 /tmp/file
$ ./io
$ chmod 400 /tmp/file
$ ls -l /tmp/file
-r-------- 1 perry perry 12 Jun 5 11:44 /tmp/file
$ ./io
io: io.c:11: main: Assertion `fd >= 0' failed.
Abort (core dumped)
$
--> perror() instead of assert()
