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Groups > comp.lang.c > #5926

Re: looking at binary files with C

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On 6/12/2011 4:47 PM, Uno wrote:
>
> There were a lot of problems with this source that needing ironing out,
> and I needed to start to somehwhere.

     An *excellent* place to start is with a description of what
you want the program to do.  As it is, you've just thrown a bunch
of code at us and expected us to divine your intentions.  If the
code were not so clearly broken, divination might stand a chance;
even then it would be better to state your purpose.  With broken
code, such a statement is even more important.

> When I've got a program that
> compiles, I like to have the magic numbers #defined.

     Your choice, but you're making extra work for yourself.  When
you're replacing numeric constants with macro names and you come
across a 3, should you change it to SHIFTS_PER_DAY or to VERSION?
Essentially, you've created a reverse-engineering problem for yourself,
giving yourself an extra opportunity to make misteaks.

> I haven't really
> done much C on a 64-bit processor, so my ballparking seems to be wanting.

     Nothing in your code stands out as bitness-related.

> #include <stdio.h>
> #include <limits.h>
> #define SIZE 20000000
> #define SIZE2 (UCHAR_MAX+1)
>
> int main(void)
> {
>     int c;
>     long counter = 0;
>     long counter2 = 0;
>     long a[SIZE2];
>     long i, j;
>     FILE *fp;
>     fp = fopen("shoulder.wmv", "rb+");

     Why the "+", since you never write to the file?  And why
is there still no check for failure, after others have already
pointed out the lack?

>     printf("UCHAR_MAX + 1 is %d\n", SIZE2);
>     for (i = 0; i < (SIZE2); ++i) {

     The parentheses around SIZE2 are harmless, but not helpful:
They're just unnecessary clutter that gives the reader more to
parse.  Perhaps you think they're necessary because SIZE2 expands
to an expression rather than to a single token?  But the expression
is already parenthesized (as good macros should be), so tacking on
an extra layer isn't needed.  What you've written is equivalent to

	for (i = 0; i < ((UCHAR_MAX+1)); ++i)

>     a[i] = 0;
>     }
>     for (j = 0; j < SIZE; ++j) {
>     c = fgetc(fp);
>     counter++;
>     if (c != EOF) {
>         a[c] = ++a[c];

     Undefined behavior: Two modifications of the same object
with no intervening sequence point.

>     } else
>         break;
>     }
>     for (i = 0; i < (SIZE2); ++i) {
>     printf("a[%ld] is %ld\n", i, a[i]);
>     counter2 = counter2 + a[i];
>     }
>     printf("Counter reached %ld\n", counter);
>     printf("Counter2 reached %ld\n", counter2);
>     fclose(fp);
>     return 0;
> }
>
> // cc -Wall -Wextra -g hist3.c -o hist
> $
>
> I needed two different SIZES, one that would be larger than the byte
> count of the file to be read and another that was one greater than
> UCHAR_MAX.

     SIZE2 (or equivalent) is necessary, yes.  But SIZE seems to
serve no useful purpose -- unless, as mentioned above, you have
purposes that aren't stated.

> Seems to behave.

     "Things are seldom what they seem.
      Skim milk masquerades as cream ..."

-- 
Eric Sosman
esosman@ieee-dot-org.invalid

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looking at binary files with C Uno <Uno@example.invalid> - 2011-06-12 00:06 -0600
  Re: looking at binary files with C Ian Collins <ian-news@hotmail.com> - 2011-06-12 18:41 +1200
    Re: looking at binary files with C Uno <Uno@example.invalid> - 2011-06-12 00:58 -0600
  Re: looking at binary files with C Barry Schwarz <schwarz45@yahoo.com> - 2011-06-12 00:05 -0700
    Re: looking at binary files with C Uno <Uno@example.invalid> - 2011-06-12 01:41 -0600
      Re: looking at binary files with C "Joachim Schmitz" <jojo.nospam@schmitz-digital.de> - 2011-06-12 11:44 +0200
      Re: looking at binary files with C Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2011-06-12 10:25 -0600
  Re: looking at binary files with C Ike Naar <ike@sverige.freeshell.org> - 2011-06-12 10:26 +0000
  Re: looking at binary files with C Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-06-12 08:23 -0400
    Re: looking at binary files with C Hans Vlems <hvlems@freenet.de> - 2011-06-13 23:48 -0700
    Re: looking at binary files with C Tim Rentsch <txr@alumni.caltech.edu> - 2011-06-23 00:55 -0700
  Re: looking at binary files with C "BartC" <bc@freeuk.com> - 2011-06-12 14:26 +0100
  Re: looking at binary files with C Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2011-06-12 10:24 -0600
    Re: looking at binary files with C Uno <Uno@example.invalid> - 2011-06-12 14:47 -0600
      Re: looking at binary files with C "BartC" <bc@freeuk.com> - 2011-06-12 22:23 +0100
        Re: looking at binary files with C Keith Thompson <kst-u@mib.org> - 2011-06-12 14:29 -0700
          Re: looking at binary files with C Uno <Uno@example.invalid> - 2011-06-12 16:31 -0600
            Re: looking at binary files with C Keith Thompson <kst-u@mib.org> - 2011-06-12 16:14 -0700
              Re: looking at binary files with C Uno <Uno@example.invalid> - 2011-06-12 18:41 -0600
      Re: looking at binary files with C Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-06-12 17:42 -0400
        Re: looking at binary files with C Uno <Uno@example.invalid> - 2011-06-12 17:01 -0600
          Re: looking at binary files with C Keith Thompson <kst-u@mib.org> - 2011-06-12 16:23 -0700
            Re: looking at binary files with C Uno <Uno@example.invalid> - 2011-06-12 17:24 -0600
              Re: looking at binary files with C Ian Collins <ian-news@hotmail.com> - 2011-06-13 11:28 +1200
                Re: looking at binary files with C Geoff <geoff@invalid.invalid> - 2011-06-12 16:52 -0700
              Re: looking at binary files with C Keith Thompson <kst-u@mib.org> - 2011-06-13 08:51 -0700
            Re: looking at binary files with C Seebs <usenet-nospam@seebs.net> - 2011-06-13 14:39 +0000
              Re: looking at binary files with C Uno <Uno@example.invalid> - 2011-06-13 20:01 -0600
                Re: looking at binary files with C Keith Thompson <kst-u@mib.org> - 2011-06-13 19:24 -0700
                Re: looking at binary files with C Seebs <usenet-nospam@seebs.net> - 2011-06-14 17:02 +0000
                Re: looking at binary files with C Uno <Uno@example.invalid> - 2011-06-16 01:32 -0600
          Re: looking at binary files with C Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-06-13 07:57 -0400
            Re: looking at binary files with C Uno <Uno@example.invalid> - 2011-06-13 20:23 -0600
              Re: looking at binary files with C Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-06-13 23:12 -0400
                Re: looking at binary files with C lovecreatesbeauty <lovecreatesbeauty@gmail.com> - 2011-06-14 01:09 -0700
          Re: looking at binary files with C Oliver Jackson <chexmofo@hotmail.com> - 2011-06-15 20:15 -0700
      Re: looking at binary files with C Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2011-06-12 18:41 -0600
      Re: looking at binary files with C James Waldby <not@valid.invalid> - 2011-06-13 01:16 +0000
        Re: looking at binary files with C Uno <Uno@example.invalid> - 2011-06-12 19:48 -0600
        Re: looking at binary files with C "io_x" <a@b.c.invalid> - 2011-06-14 12:19 +0200
          Re: looking at binary files with C lovecreatesbeauty <lovecreatesbeauty@gmail.com> - 2011-06-14 03:58 -0700
            Re: looking at binary files with C "io_x" <a@b.c.invalid> - 2011-06-14 19:07 +0200
              Re: looking at binary files with C "io_x" <a@b.c.invalid> - 2011-06-14 19:46 +0200
              Re: looking at binary files with C Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2011-06-14 16:08 -0600
          Re: looking at binary files with C Ian Collins <ian-news@hotmail.com> - 2011-06-15 08:47 +1200
      Re: looking at binary files with C Hans Vlems <hvlems@freenet.de> - 2011-06-13 23:51 -0700
  Re: looking at binary files with C Michael Press <rubrum@pacbell.net> - 2011-06-15 13:06 -0700
    Re: looking at binary files with C Uno <Uno@example.invalid> - 2011-06-16 01:38 -0600
      Re: looking at binary files with C Michael Press <rubrum@pacbell.net> - 2011-06-16 00:54 -0700
        Re: looking at binary files with C James Waldby <not@valid.invalid> - 2011-06-16 16:59 +0000
      Re: looking at binary files with C "J. J. Farrell" <jjf@bcs.org.uk> - 2011-06-16 18:32 +0100

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