Differences between version 4 and previous revision of fcntl(2).
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| Newer page: | version 4 | Last edited on Sunday, November 3, 2002 3:12:33 pm | by PerryLorier | Revert |
| Older page: | version 3 | Last edited on Sunday, November 3, 2002 2:54:57 pm | by PerryLorier | Revert |
@@ -93,7 +93,102 @@
!!CONFORMING TO
SVr4, SVID, POSIX, X/OPEN, BSD 4.3. Only the operations F_DUPFD, F_GETFD, F_SETFD, F_GETFL, F_SETFL, F_GETLK, F_SETLK and F_SETLKW are specified in POSIX.1. F_GETOWN and F_SETOWN are BSDisms not supported in SVr4; F_GETSIG and F_SETSIG are specific to Linux. The flags legal for F_GETFL/F_SETFL are those supported by open(2) and vary between these systems; O_APPEND, O_NONBLOCK, O_RDONLY, and O_RDWR are specified in POSIX.1. SVr4 supports several other options and flags not documented here.
SVr4 documents additional [EIO], [ENOLINK] and [EOVERFLOW] error conditions.
+
+!!EXAMPLES
+ /*
+ * This program demonstrates using fcntl(2) similar to dup(2)
+ */
+
+ #include <sys/stat.h> /* for S_* constants */
+ #include <unistd.h> /* write(2), close(2) prototype */
+ #include <fcntl.h> /* fcntl(2), creat(2) prototypes, F_* constants */
+ #include <stdio.h> /* fprintf(3), stderr prototype */
+ #include <string.h> /* strerror(3) prototype */
+ #include <errno.h> /* for errno prototype */
+
+ #define FILENAME "/tmp/fcntl_dup.example"
+
+ /*
+ * Input:
+ * fd: a file descriptor to write to
+ * msg: A message to write
+ * Returns:
+ * 0: success
+ * non 0: error (error message already written to stderr)
+ */
+ int do_write(int fd,char *msg)
+ {
+ int err;
+
+ err=write(fd,msg,strlen(msg));
+
+ if (err==-1) {
+ fprintf(
+ stderr,
+ "write(fd,\"%s\",strlen(\"%s\")): %s (%i)\n",
+ msg,
+ msg,
+ strerror(errno),
+ errno);
+ return 1;
+ }
+
+ if (err!=strlen(msg)) {
+ fprintf(
+ stderr,
+ "write did not write the full length, and I'm too dumb to try again\n"
+ );
+ return 1;
+ }
+ return 0;
+ }
+
+ int main(int argc,char **argv)
+ {
+ int fd;
+ int fd2;
+
+ fd=creat(FILENAME,S_IRUSR|S_IWUSR);
+ if (fd==-1) {
+ fprintf(
+ stderr,
+ "creat(\"%s\",S_IRUSR|S_IWUSR): %s (%i)\n",
+ FILENAME,
+ strerror(errno),
+ errno);
+ return 1;
+ }
+
+ if (do_write(fd,"This is some sample text\n")!=0) {
+ return 1;
+ }
+
+ /* Now, use fcntl to create a new fd, greater or equal to 0 */
+ fd2 = fcntl(fd,F_DUPFD,0);
+
+ if (fd2 == -1) {
+ fprintf(
+ stderr,
+ "fcntl(fd,F_DUPFD,0): %s (%i)\n",
+ strerror(errno),
+ errno);
+ return 1;
+ }
+
+ if (do_write(fd2,"This proves that fd2 is working\n")!=0) {
+ return 1;
+ }
+
+ if (do_write(fd,"This proves that fd's file pointer has been moved by fd2 "
+ "writing to the socket\n")!=0) {
+ return 1;
+ }
+
+ close(fd);
+ close(fd2);
+ return 0;
+ }
!!SEE ALSO
dup2(2), flock(2), open(2), socket(2)
