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Re: Method other than strlen to check for truncation with fgets?

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Siri Cruz <chine.bleu@yahoo.com> writes:
> In article <878ud0jjri.fsf@kst-u.example.com>, Keith Thompson <kst-u@mib.org> 
> wrote:
>> Siri Cruz <chine.bleu@yahoo.com> writes:
>> > In article <midqe0$62n$1@dont-email.me>, mathog <dmathog@gmail.com> wrote:
>> >> It should work when the input line is truncated.  The problem is that,
>> >> from my reading of the fgets man page, there is no guarantee that the 
>> >> library will not write something beyond the \0 in the buffer.  I don't 
>> >> expect that would happen, but also do not see anything saying that it 
>> >> cannot.
>> >
>> > If this is critical to you, use fgetline instead.
>> >
>> > /*
>> >     Read and return the next line from input.
>> >     The line is mallocked; caller is responsibile for freeing.
>> >     The line ends in \n if the line from the input file did.
>> >     Returns NULL on EOF.
>> > */
>> >
>> > char *fgetline (FILE *input) {
>> >     int c; char *line = NULL; int m = 0, n = 0;
>> >     while ((c=fgetc(input))!=EOF) {
>> >         if (c==0) abort();
>> >         if (n+1>=m) {m = 2*(n+1); line = realloc(line, m);}
>> >         if (!line) abort();
>
> Ummm.......

Ok, I didn't notice that.  I'd suggest returning NULL or some other
error indication on an allocation failure.

Assigning the result of realloc() to the same pointer object you pass to
it means that if the reallocation fails, you've just lost the pointer
to the original data, which is still there.  If your response is to
abort the program, that doesn't necessarily matter.

>> >         line[n++] = c;
>> >         if (c=='\n') break;
>> >     }
>> >     if (line) {line = realloc(line, n+1); line[n] = 0;}

And this allocation is not checked.

>> >     return line;
>> > }
>> 
>> This doesn't check for allocation failures.

-- 
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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Method other than strlen to check for truncation with fgets? mathog <dmathog@gmail.com> - 2015-05-06 12:35 -0700
  Re: Method other than strlen to check for truncation with fgets? Barry Schwarz <schwarzb@dqel.com> - 2015-05-06 15:14 -0700
    Re: Method other than strlen to check for truncation with fgets? mathog <dmathog@gmail.com> - 2015-05-06 16:14 -0700
      Re: Method other than strlen to check for truncation with fgets? Barry Schwarz <schwarzb@dqel.com> - 2015-05-06 17:51 -0700
      Re: Method other than strlen to check for truncation with fgets? Tim Rentsch <txr@alumni.caltech.edu> - 2015-05-06 18:23 -0700
        Re: Method other than strlen to check for truncation with fgets? mathog <dmathog@gmail.com> - 2015-05-07 10:07 -0700
          Re: Method other than strlen to check for truncation with fgets? Tim Rentsch <txr@alumni.caltech.edu> - 2015-05-07 16:06 -0700
  Re: Method other than strlen to check for truncation with fgets? James Kuyper <jameskuyper@verizon.net> - 2015-05-06 22:20 -0400
    Re: Method other than strlen to check for truncation with fgets? mathog <dmathog@gmail.com> - 2015-05-07 10:29 -0700
      Re: Method other than strlen to check for truncation with fgets? James Kuyper <jameskuyper@verizon.net> - 2015-05-07 14:09 -0400
        Re: Method other than strlen to check for truncation with fgets? mathog <dmathog@gmail.com> - 2015-05-07 12:48 -0700
          Re: Method other than strlen to check for truncation with fgets? James Kuyper <jameskuyper@verizon.net> - 2015-05-07 17:01 -0400
            Re: Method other than strlen to check for truncation with fgets? mathog <dmathog@gmail.com> - 2015-05-08 10:59 -0700
              Re: Method other than strlen to check for truncation with fgets? James Kuyper <jameskuyper@verizon.net> - 2015-05-08 14:48 -0400
              Re: Method other than strlen to check for truncation with fgets? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-05-08 18:37 +0000
                Re: Method other than strlen to check for truncation with fgets? James Kuyper <jameskuyper@verizon.net> - 2015-05-08 15:06 -0400
  Re: Method other than strlen to check for truncation with fgets? Lőrinczy Zsigmond <nospam@for.me> - 2015-05-07 07:04 +0200
    Re: Method other than strlen to check for truncation with fgets? Richard Heathfield <rjh@cpax.org.uk> - 2015-05-07 06:52 +0100
      Re: Method other than strlen to check for truncation with fgets? Lőrinczy Zsigmond <zsiga@nospam.for.me> - 2015-05-07 09:58 +0200
        Re: Method other than strlen to check for truncation with fgets? Stephen Sprunk <stephen@sprunk.org> - 2015-05-07 09:12 -0500
        Re: Method other than strlen to check for truncation with fgets? Keith Thompson <kst-u@mib.org> - 2015-05-07 08:51 -0700
          Re: Method other than strlen to check for truncation with fgets? Lőrinczy Zsigmond <zsiga@nospam.for.me> - 2015-05-07 19:09 +0200
            Re: Method other than strlen to check for truncation with fgets? James Kuyper <jameskuyper@verizon.net> - 2015-05-07 14:15 -0400
    Re: Method other than strlen to check for truncation with fgets? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-05-07 11:31 +0100
      Re: Method other than strlen to check for truncation with fgets? Lőrinczy Zsigmond <zsiga@nospam.for.me> - 2015-05-07 15:41 +0200
        Re: Method other than strlen to check for truncation with fgets? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-05-08 02:44 +0100
          Re: Method other than strlen to check for truncation with fgets? James Kuyper <jameskuyper@verizon.net> - 2015-05-07 23:24 -0400
            Re: Method other than strlen to check for truncation with fgets? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-05-08 04:41 +0100
      Re: Method other than strlen to check for truncation with fgets? Keith Thompson <kst-u@mib.org> - 2015-05-07 08:49 -0700
        Re: Method other than strlen to check for truncation with fgets? James Kuyper <jameskuyper@verizon.net> - 2015-05-07 12:19 -0400
        Re: Method other than strlen to check for truncation with fgets? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-05-07 18:08 +0000
    Re: Method other than strlen to check for truncation with fgets? James Kuyper <jameskuyper@verizon.net> - 2015-05-07 12:19 -0400
      Re: Method other than strlen to check for truncation with fgets? mathog <dmathog@gmail.com> - 2015-05-07 09:57 -0700
  Re: Method other than strlen to check for truncation with fgets? Siri Cruz <chine.bleu@yahoo.com> - 2015-05-07 11:31 -0700
    Re: Method other than strlen to check for truncation with fgets? Keith Thompson <kst-u@mib.org> - 2015-05-07 12:00 -0700
      Re: Method other than strlen to check for truncation with fgets? Siri Cruz <chine.bleu@yahoo.com> - 2015-05-07 12:44 -0700
        Re: Method other than strlen to check for truncation with fgets? Keith Thompson <kst-u@mib.org> - 2015-05-07 14:03 -0700
          Re: Method other than strlen to check for truncation with fgets? Siri Cruz <chine.bleu@yahoo.com> - 2015-05-07 15:28 -0700

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