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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: Method other than strlen to check for truncation with fgets?
Date: Thu, 07 May 2015 12:00:01 -0700
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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();
>         line[n++] = c;
>         if (c=='\n') break;
>     }
>     if (line) {line = realloc(line, n+1); line[n] = 0;}
>     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"