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Tim
Tim

Reputation: 99606

Can multiple `FILE` objects share the same file descriptor?

From APUE

Each standard I/O stream (i.e. each FILE object) has an associated file descriptor.

In a program, can multiple FILE objects share the same file descriptor?

If yes, is it done by calling fdopen() multiple times with the same given file descriptor, each of which returns a pointer to a different FILE object?

If I flcose() on a pointer to a given FILE object, will the file descriptor of the FILE object still exists and connects to the file, if there is another FILE object sharing the same file descriptor?

Thanks.

Upvotes: 2

Views: 1230

Answers (1)

R.. GitHub STOP HELPING ICE
R.. GitHub STOP HELPING ICE

Reputation: 215617

Yes, but it's a very bad idea, since fclose closes the associated fd, and therefore yyou can only fclose one of them without it resulting in close on a file descriptor that no longer belongs to the FILE, and may have been reassigned for other use. In principle this happens even at process termination, unless you use _exit/_Exit or abnormal termination.

A related question is whether you can use different file descriptors (each produced by dup for the same underlying open file description with more than one file. For that, the answer is also yes, and while it may be a bad idea, there are rules POSIX specifies that make it safe if you follow them:

2.5.1 Interaction of File Descriptors and Standard I/O Streams

Upvotes: 3

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