Re: LINE_MAX

[Lennart Jablonka <vol@ljabl.com>]

Quoth Alejandro Colomar:
>I think I found a bug in POSIX.1-2017 (and probably, previous ones too,
>but didn't check).
>
><https://pubs.opengroup.org/onlinepubs/009695399/basedefs/limits.h.html>:
>     {LINE_MAX}
>           Unless  otherwise  noted, the maximum length, in bytes, of a
>           utility’s input  line  (either  standard  input  or  another
>           file),  when  the  utility  is  described as processing text
>           files. The length includes room for the trailing <newline>.
>           Minimum Acceptable Value: {_POSIX2_LINE_MAX}
>
>It doesn't say anything about the trailing null byte for the buffer that
>holds it, but I assume it doesn't include it, from the context.
>
>However:
><https://pubs.opengroup.org/onlinepubs/009695399/functions/fgets.html>:
>The following sections are informative.
>EXAMPLES
>
>    Reading Input
>
>    The following example uses fgets() to read each line of input. {LINE_MAX}, which defines the maximum size of the input line, is defined in the <limits.h> header.
>
>    #include <stdio.h>
>    ...
>    char line[LINE_MAX];
>    ...
>    while (fgets(line, LINE_MAX, fp) != NULL) {
>    ...
>    }
>    ...
>
>
>This example seems to contradict my understanding of what limits.h says.
>
>So, either limits.h should be explicit that the trailing null byte is
>also included in LINE_MAX, or the example is bogus and should be fixed.
>I guess it's the latter, although I wish it was the former, so we can
>avoid a +1 in the code.
>
>In any case, could you please forward this to the Austin group?

Good find.  You aren’t the first one to find it: 
https://austingroupbugs.net/view.php?id=182 discusses that 
example a little.  The desired action written there appears 
verbatim (bar formatting) in the 4.1 draft of POSIX.1-202x.