Flush stdin?

**Tom Zych** · Nov 13 '05, 06:04 PM

Re: Flush stdin?

Jonathan Neill wrote:
[color=blue]
> I'm aware that there is no ANSI (or POSIX, or any standard, to my knowledge)
> way of flushing stdin or any other application-level input buffer, but if
> anyone knows a hack or a non-portable way to do this, no matter how obscure
> or arcane, I'd appreciate it.[/color]

Um...what does it mean, to flush an input buffer?

If you mean you want to read and discard whatever's in the buffer at
a certain time, under POSIX I suppose you could use non-blocking
reads until they come up empty. I don't think standard C has
non-blocking I/O, does it?

If you mean you want to wipe the buffer's memory space, because the
user entered a password or something, I'd avoid using stdin for such
purposes.

--
Tom Zych
This email address will expire at some point to thwart spammers.
Permanent address: echo 'gbzmlpu@cbobk. pbz' | rot13

**Ricardo Bugalho** · Nov 13 '05, 06:04 PM

Re: Flush stdin?

I agree. In any case, he can try setbuf() to use non-buffered streams.

--
Ricardo

**August Derleth** · Nov 13 '05, 06:04 PM

Re: Flush stdin?

"Jonathan Neill" <TYR124840@tyle r.net> wrote in
news:vlfp829sfd in97@corp.super news.com on Thu 04 Sep 2003 07:16:14p:
[color=blue]
> I'm aware that there is no ANSI (or POSIX, or any standard, to my
> knowledge) way of flushing stdin or any other application-level input
> buffer, but if anyone knows a hack or a non-portable way to do this, no
> matter how obscure or arcane, I'd appreciate it.
>
>[/color]

You'd do better asking on a system-specific newsgroup. The geeks there
will know a dozen ways to do this on your specific system (or will know if
it can't be done at all). Here, we deal with Standard C, not any system-
specific extensions to the language. If you have a question about ANSI/ISO
C (up to and including C99, and even including pre-Standard K&R C if you
still need it), this is the best place to ask it. If you want to do
something that is system-specific, ask on a system-specific newsgroup for
the best answers.

http://www.eskimo.com/~scs/C-faq/s19.html -- A list of answers to
questions that can't be answered in Standard C. Read the (rest of the) FAQ
for more info.

**Richard Heathfield** · Nov 13 '05, 06:05 PM

Re: Flush stdin?

Jonathan Neill wrote:
[color=blue]
> I'm aware that there is no ANSI (or POSIX, or any standard, to my
> knowledge) way of flushing stdin or any other application-level input
> buffer, but if anyone knows a hack or a non-portable way to do this, no
> matter how obscure or arcane, I'd appreciate it.[/color]

What do you mean by "flush"? If you mean that you want to discard the
current character and all subsequent characters until exactly one \n has
been discarded (and this is typically what most people want from a
so-called "flush" of stdin), call this function:

#include <stdio.h>

/* constraint: fp must be open for input */
int fpDrain(FILE *fp)
{
int ch = 0;
while((ch = getc(fp)) != EOF && ch != '\n')
{
continue;
}
return EOF == ch;
}

--
Richard Heathfield : binary@eton.pow ernet.co.uk
"Usenet is a strange place." - Dennis M Ritchie, 29 July 1999.
C FAQ: http://www.eskimo.com/~scs/C-faq/top.html
K&R answers, C books, etc: http://users.powernet.co.uk/eton

**Stephan Wilms** · Nov 13 '05, 06:05 PM

Re: Flush stdin?

Hi,

The problem with non portable solutions is that they tend to be highly
system specific. The solution to the problem must be tailored to the
specifics of the systems where it is intended to be used. Since you
did not describe your system / environment we can not give you a
specific working solution.

For instance there are systems where "fflush(stdin); " actually works
and does what you want (e.g. Microsoft Visual C). Another solution
would indeed be to check your system for a non blocking function to
read from a stream or terminal. To add to the already existant obscure
examples: Microsoft C offers a function called "_kbhit()" to check if
there is pending keyboard input available.

--
Stephan Wilms

"Jonathan Neill" <TYR124840@tyle r.net> wrote in message news:<vlfp829sf din97@corp.supe rnews.com>...[color=blue]
> I'm aware that there is no ANSI (or POSIX, or any standard, to my knowledge)
> way of flushing stdin or any other application-level input buffer, but if
> anyone knows a hack or a non-portable way to do this, no matter how obscure
> or arcane, I'd appreciate it.[/color]

**Martin Ambuhl** · Nov 13 '05, 06:05 PM

Re: Flush stdin?

Jonathan Neill wrote:
[color=blue]
> I'm aware that there is no ANSI (or POSIX, or any standard, to my knowledge)
> way of flushing stdin or any other application-level input buffer, but if
> anyone knows a hack or a non-portable way to do this, no matter how obscure
> or arcane, I'd appreciate it.[/color]

It doesn't even mean anything. Read the description of the action of
fflush() on output streams and try to come up with a reasonable analogy for
input streams.

--
Martin Ambuhl

**Alex Vinokur** · Nov 13 '05, 06:05 PM

Re: Flush stdin?

"Jonathan Neill" <TYR124840@tyle r.net> wrote in message news:vlfp829sfd in97@corp.super news.com...[color=blue]
> I'm aware that there is no ANSI (or POSIX, or any standard, to my knowledge)
> way of flushing stdin or any other application-level input buffer, but if
> anyone knows a hack or a non-portable way to do this, no matter how obscure
> or arcane, I'd appreciate it.
>
>[/color]
Look at :

http://groups.google.com/groups?selm=b5skqr%242d7uag%241%40ID-79865.news.dfncis.de

http://alexvn.freeservers.com/s1/download.html (Flushing non-read input data with using tcflush)

=============== =============== =======
Alex Vinokur
mailto:alexvn@c onnect.to

http://mathforum.org/library/view/10978.html

=============== =============== =======

**Richard Heathfield** · Nov 13 '05, 06:05 PM

Re: Flush stdin?

Jonathan Neill wrote:
[color=blue]
> I'm aware that there is no ANSI (or POSIX, or any standard, to my
> knowledge) way of flushing stdin or any other application-level input
> buffer, but if anyone knows a hack or a non-portable way to do this, no
> matter how obscure or arcane, I'd appreciate it.[/color]

What do you mean by "flush"? If you mean that you want to discard the
current character and all subsequent characters until exactly one \n has
been discarded (and this is typically what most people want from a
so-called "flush" of stdin), call this function:

#include <stdio.h>

/* constraint: fp must be open for input */
int fpDrain(FILE *fp)
{
int ch = 0;
while((ch = getc(fp)) != EOF && ch != '\n')
{
continue;
}
return EOF == ch;
}

--
Richard Heathfield : binary@eton.pow ernet.co.uk
"Usenet is a strange place." - Dennis M Ritchie, 29 July 1999.
C FAQ: http://www.eskimo.com/~scs/C-faq/top.html
K&R answers, C books, etc: http://users.powernet.co.uk/eton

**Stephan Wilms** · Nov 13 '05, 06:06 PM

Re: Flush stdin?

Hi,

The problem with non portable solutions is that they tend to be highly
system specific. The solution to the problem must be tailored to the
specifics of the systems where it is intended to be used. Since you
did not describe your system / environment we can not give you a
specific working solution.

For instance there are systems where "fflush(stdin); " actually works
and does what you want (e.g. Microsoft Visual C). Another solution
would indeed be to check your system for a non blocking function to
read from a stream or terminal. To add to the already existant obscure
examples: Microsoft C offers a function called "_kbhit()" to check if
there is pending keyboard input available.

--
Stephan Wilms

"Jonathan Neill" <TYR124840@tyle r.net> wrote in message news:<vlfp829sf din97@corp.supe rnews.com>...[color=blue]
> I'm aware that there is no ANSI (or POSIX, or any standard, to my knowledge)
> way of flushing stdin or any other application-level input buffer, but if
> anyone knows a hack or a non-portable way to do this, no matter how obscure
> or arcane, I'd appreciate it.[/color]

**Martin Ambuhl** · Nov 13 '05, 06:06 PM

Re: Flush stdin?

Jonathan Neill wrote:
[color=blue]
> I'm aware that there is no ANSI (or POSIX, or any standard, to my knowledge)
> way of flushing stdin or any other application-level input buffer, but if
> anyone knows a hack or a non-portable way to do this, no matter how obscure
> or arcane, I'd appreciate it.[/color]

It doesn't even mean anything. Read the description of the action of
fflush() on output streams and try to come up with a reasonable analogy for
input streams.

--
Martin Ambuhl

**Tom Zych** · Nov 13 '05, 06:06 PM

Re: Flush stdin?

Stephan Wilms wrote:
[color=blue]
> The problem with non portable solutions is that they tend to be highly
> system specific.[/color]

<captious>

Really? Gosh. I guess that's why they're non-portable, then?

</captious>

--
Tom Zych
This email address will expire at some point to thwart spammers.
Permanent address: echo 'gbzmlpu@cbobk. pbz' | rot13

**Alex Vinokur** · Nov 13 '05, 06:06 PM

Re: Flush stdin?

"Jonathan Neill" <TYR124840@tyle r.net> wrote in message news:vlfp829sfd in97@corp.super news.com...[color=blue]
> I'm aware that there is no ANSI (or POSIX, or any standard, to my knowledge)
> way of flushing stdin or any other application-level input buffer, but if
> anyone knows a hack or a non-portable way to do this, no matter how obscure
> or arcane, I'd appreciate it.
>
>[/color]
Look at :

http://groups.google.com/groups?selm=b5skqr%242d7uag%241%40ID-79865.news.dfncis.de

http://alexvn.freeservers.com/s1/download.html (Flushing non-read input data with using tcflush)

=============== =============== =======
Alex Vinokur
mailto:alexvn@c onnect.to

http://mathforum.org/library/view/10978.html

=============== =============== =======

**Tom Zych** · Nov 13 '05, 06:06 PM

Re: Flush stdin?

Stephan Wilms wrote:
[color=blue]
> The problem with non portable solutions is that they tend to be highly
> system specific.[/color]

<captious>

Really? Gosh. I guess that's why they're non-portable, then?

</captious>

--
Tom Zych
This email address will expire at some point to thwart spammers.
Permanent address: echo 'gbzmlpu@cbobk. pbz' | rot13

**The Real OS/2 Guy** · Nov 13 '05, 06:08 PM

Re: Flush stdin?

On Fri, 5 Sep 2003 01:16:14 UTC, "Jonathan Neill"
<TYR124840@tyle r.net> wrote:
[color=blue]
> I'm aware that there is no ANSI (or POSIX, or any standard, to my knowledge)
> way of flushing stdin or any other application-level input buffer, but if
> anyone knows a hack or a non-portable way to do this, no matter how obscure
> or arcane, I'd appreciate it.[/color]

100% ANSI compatible:

/* flush stdin */
/* params: */
/* int c int to hold temorary readed char from stdin */
/* */
/* read from stdin until end of file or end of line reached */
#define FLUSHIN(c) while ((c = getc() != EOF && c != '\n')

stdin is commonly line buffered or unbuffered. In both cases reading
until '\n' is dedected is flushing the input stream. Even when stdin
is set to be block buffered (e.g. as pipe or file it makes sense to
"flush". Because stdin is a text stram, so reading until '\n'
syncronises the stream so that the next coming char will be the first
of a line.

--
Tschau/Bye
Herbert

eComStation 1.1 Deutsch Beta ist verügbar

Flush stdin?

Flush stdin?

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment