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Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead?

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rivkaumiller@gmail.com writes:
[...]
> I finally found this worked well
>
> while (fscanf ( FpSource, "%d" , &input ) != EOF){
>>   // do certain actions with "input"
>> }
>
> as all it cares about is reaching the end of the input file.
[...]

Ok, let's try that:

#include <stdio.h>
#include <stdlib.h>
int main(void) {
    long count = 0;
    FILE *FpSource = fopen("/etc/motd", "r");
    int input;

    if (FpSource == NULL) {
        fprintf(stderr, "Failed to open file\n");
        exit(EXIT_FAILURE);
    }

    while (fscanf ( FpSource, "%d" , &input ) != EOF) {
        count ++;
        if (count >= 1000000) {
            fprintf(stderr, "You didn't really want an infinite loop, did you?\n");
            exit(EXIT_FAILURE);
        }
    }
    fclose(FpSource);
}

The output on my system was "You didn't really want an infinite loop,
did you?".

The first line of /etc/motd on my system starts with the word "Welcome",
which is not an optionally signed decimal integer.  When fscanf() with a
"%d" format sees that, it returns 0 (to denote the number of items it
was able to read) and leaves the entire line waiting to be read by the
next input call -- which is the fscanf() call in the next iteration of
the same loop.

fprintf() returns the number of items you asked it to read (1 in this
case) if it was successful, some value less than that if it was
unsuccessful, or EOF if an input failure occurs before the first value
has completed.  You have to allow for all those possibilities.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

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Thread

How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? rivkaumiller@gmail.com - 2014-03-30 19:04 -0700
  Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? Richard Damon <Richard@Damon-Family.org> - 2014-03-30 22:31 -0400
    Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? rivkaumiller@gmail.com - 2014-03-30 19:43 -0700
      Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? Richard Damon <Richard@Damon-Family.org> - 2014-03-30 23:09 -0400
  Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? rivkaumiller@gmail.com - 2014-03-30 19:35 -0700
  Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? rivkaumiller@gmail.com - 2014-03-30 19:47 -0700
    Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? "BartC" <bc@freeuk.com> - 2014-03-31 11:53 +0100
      Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-31 17:50 +0000
        Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? Kaz Kylheku <kaz@kylheku.com> - 2014-03-31 18:55 +0000
          Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? "BartC" <bc@freeuk.com> - 2014-03-31 22:51 +0100
            Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? Kaz Kylheku <kaz@kylheku.com> - 2014-03-31 22:46 +0000
              Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? "BartC" <bc@freeuk.com> - 2014-04-01 00:03 +0100
              Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-03-31 20:33 -0400
                Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? "BartC" <bc@freeuk.com> - 2014-04-01 09:35 +0100
                Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? Keith Thompson <kst-u@mib.org> - 2014-04-01 07:35 -0700
                Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? "BartC" <bc@freeuk.com> - 2014-04-01 17:19 +0100
                Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? Keith Thompson <kst-u@mib.org> - 2014-04-01 10:14 -0700
                Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? "BartC" <bc@freeuk.com> - 2014-04-01 18:59 +0100
                Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? Öö Tiib <ootiib@hot.ee> - 2014-04-04 00:29 -0700
                Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? "BartC" <bc@freeuk.com> - 2014-04-04 12:35 +0100
                Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? Seungbeom Kim <musiphil@bawi.org> - 2014-04-08 11:48 -0700
                Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? Öö Tiib <ootiib@hot.ee> - 2014-04-08 15:52 -0700
                Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-04-02 18:38 +0000
                Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? Keith Thompson <kst-u@mib.org> - 2014-04-02 11:48 -0700
                Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-04-02 23:18 +0000
                Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? Kaz Kylheku <kaz@kylheku.com> - 2014-04-03 00:05 +0000
                Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? James Kuyper <jameskuyper@verizon.net> - 2014-04-02 21:12 -0400
                Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? Keith Thompson <kst-u@mib.org> - 2014-04-02 19:16 -0700
                Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-04-03 03:16 +0000
                Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? James Kuyper <jameskuyper@verizon.net> - 2014-04-02 15:07 -0400
                Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-04-01 23:00 +0100
                Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? Seungbeom Kim <musiphil@bawi.org> - 2014-04-08 11:56 -0700
            Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2014-04-01 02:14 +0300
            Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-04-01 04:52 +0000
              Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? "BartC" <bc@freeuk.com> - 2014-04-01 09:56 +0100
  Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-03-30 22:49 -0400
  Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? James Kuyper <jameskuyper@verizon.net> - 2014-03-30 22:58 -0400
    Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? rivkaumiller@gmail.com - 2014-03-31 09:10 -0700
      Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? James Kuyper <jameskuyper@verizon.net> - 2014-03-31 12:25 -0400
      Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? Keith Thompson <kst-u@mib.org> - 2014-03-31 10:56 -0700
  Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? James Kuyper <jameskuyper@verizon.net> - 2014-03-30 23:09 -0400
  Re: How to modify ((c=getchar())!=NULL) to use fscanf or scanf instead? Keith Thompson <kst-u@mib.org> - 2014-03-31 08:55 -0700

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