Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.c > #24353

Re: scanf()

Show all headers | View raw

Ben Bacarisse wrote:

> Edward Rutherford <edward.p.rutherford79@REMOVETHIS.gmail.com> writes:
> 
>> If scanf() fails for a matching error, what can we say about the
>> location of the file pointer for subsequent reads from stdin? Could it
>> have read on through an indeterminate amount of stdin, or will it
>> always be positioned immediately after the last successful conversion
>> from the format string?
> 
> No, it can read an unlimited number of characters before reporting a
> matching failure.  There are lots of details, but since you are asking
> an all-or-nothing question, you probably don't care about them.  A
> "worst case" example occurs when processing "%d" -- an unlimited number
> of white-space characters can be read before any matching failure can be
> reported.  If there is such a failure, the character that causes it
> matching failure will pushed back onto the stream, but that's all.
> 
> The scanf functions only ever push back at most one character so you can
> use that a rule of thumb to imagine what they must consume before a
> directive can fail.
> 
> For some input patterns %n is an effective solution, but you don't say
> what your overall objective is so I can't be sure.

That's unfortunate, because then there's no way to recover the non-
matching data, as far as I can see.

Wouldn't it be better if scanf() buffered non-matching characters, either 
seemlessly in the background (so that future reads from stdin saw those 
characters) or by returning a pointer to a buffer containing them?

Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

scanf() Edward Rutherford <edward.p.rutherford79@REMOVETHIS.gmail.com> - 2012-08-06 20:58 +0000
  Re: scanf() Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-08-06 17:29 -0400
    Re: scanf() Keith Thompson <kst-u@mib.org> - 2012-08-06 14:40 -0700
  Re: scanf() James Kuyper <jameskuyper@verizon.net> - 2012-08-06 17:39 -0400
  Re: scanf() Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-08-06 22:49 +0100
    Re: scanf() Edward Rutherford <edward.p.rutherford79@REMOVETHIS.gmail.com> - 2012-08-07 18:37 +0000
      Re: scanf() James Kuyper <jameskuyper@verizon.net> - 2012-08-07 15:01 -0400
      Re: scanf() Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-08-07 15:03 -0400
      Re: scanf() Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-08-07 20:51 +0100
      Re: scanf() John Bode <jfbode1029@gmail.com> - 2012-08-09 14:00 -0700
        Re: scanf() Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-08-11 03:08 -0700
          Re: scanf() Keith Thompson <kst-u@mib.org> - 2012-08-11 10:40 -0700
            Re: scanf() Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-08-11 13:34 -0700
              Re: scanf() "BartC" <bc@freeuk.com> - 2012-08-11 23:04 +0100
              Re: scanf() James Kuyper <jameskuyper@verizon.net> - 2012-08-11 19:20 -0400
              Re: scanf() Keith Thompson <kst-u@mib.org> - 2012-08-11 17:30 -0700
                Re: scanf() Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-08-11 20:41 -0400
                Re: scanf() Keith Thompson <kst-u@mib.org> - 2012-08-11 18:13 -0700
                Re: scanf() Keith Thompson <kst-u@mib.org> - 2012-08-11 18:16 -0700
                Re: scanf() Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-08-11 21:32 -0400
                Re: scanf() Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-08-12 04:07 -0700
                Re: scanf() James Kuyper <jameskuyper@verizon.net> - 2012-08-12 08:03 -0400
                Re: scanf() Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-08-12 06:41 -0700
                Re: scanf() Keith Thompson <kst-u@mib.org> - 2012-08-12 13:39 -0700
                Re: scanf() Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-08-12 14:20 -0700
                Re: scanf() Keith Thompson <kst-u@mib.org> - 2012-08-12 16:33 -0700
                Re: scanf() "Heinrich Wolf" <invalid@invalid.invalid> - 2012-08-13 12:22 +0200
                Re: scanf() Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-09-05 00:13 +0300
                Re: scanf() Tim Rentsch <txr@alumni.caltech.edu> - 2012-09-07 14:18 -0700
                Re: scanf() Keith Thompson <kst-u@mib.org> - 2012-09-07 15:02 -0700
                Re: scanf() Tim Rentsch <txr@alumni.caltech.edu> - 2012-09-07 17:25 -0700
                Re: scanf() Keith Thompson <kst-u@mib.org> - 2012-09-07 18:35 -0700
              Re: scanf() Seungbeom Kim <musiphil@bawi.org> - 2012-08-12 21:05 -0700
        Re: scanf() Robert Wessel <robertwessel2@yahoo.com> - 2012-08-11 17:37 -0500

csiph-web