Why won't fflush(stdin) work?

Question

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Using fflush(stdin)

My code is:

scanf("%d", &_choice);
fflush(stdin);
gets(input);

I use fflush(stdin); to remove the '\n' character that was left after scanf.

However, I found out that it doesn't work, and gets automatically takes the '\n' char and continues.

I solved it by using getchar() instead of fflush but I still can't figure out why didn't fflush work...

Edit: I understand now fflush is for output streams only. But is there a command for "cleaning" stdin from junk?

@milleniumbug I don't want to deal with removing last `\n` character — cookya, Jan 13 '13 at 00:13
@cookya You prefer buffer overruns? Also, `gets()` has finally been removed from the language. — Daniel Fischer, Jan 13 '13 at 00:16
[What to use instead](http://stackoverflow.com/a/6277391/1012936) — milleniumbug, Jan 13 '13 at 00:31

score 4 · Accepted Answer · answered Jan 13 '13 at 00:00

4

Because fflush is for output streams.

And at any rate, fflush is not for "removing \n characters"...

answered Jan 13 '13 at 00:00

Then what does `fflush(stdin)` do? And how can `\n` characters be moved from stdin / stdout ? – cookya Jan 13 '13 at 00:01
1

@cookya It's an error. `fflush` writes buffered data (i.e. data that hasn't been written yet) to the specified output stream. `stdin` is not an output stream. – melpomene Jan 13 '13 at 00:02
1

@cookya: It's undefined behaviour; anything could happen. – Oliver Charlesworth Jan 13 '13 at 00:02
For what it's worth, `fflush(stdin)` *is defined* on POSIX systems, but only in the case where `stdin` is seekable. It's undefined for unseekable streams. This is of course really stupid... – R.. GitHub STOP HELPING ICE Jan 13 '13 at 04:26

1 Answers1