[Bug libc/5468] New: Error in getline(3) manpage

[Bug libc/5468] New: Error in getline(3) manpage

[luke dot hutch at mit dot edu]

The getline(3) manpage states:

       ssize_t getline(char **lineptr, size_t *n, FILE *stream);
 [...]
       If  *lineptr  is  NULL,  then getline() will allocate a buffer for
storing the line, which should be
       freed by the user program.  (The value in *n is ignored.)

Based on this description (particularly the part that says the value *n is
ignored), you should be able to do something like:

    char *line = NULL;
    getline(&line, NULL, stream);

However this always fails, because the code for getline does the following:

  if (!lineptr || !n || !stream)
    {
      errno = EINVAL;
      return -1;
    }

  if (!*lineptr)
    {
      *n = MIN_CHUNK;
      *lineptr = malloc (*n);
      if (!*lineptr)
	{
	  errno = ENOMEM;
	  return -1;
	}
      *lineptr[0] = '\0';
    }

(thus the !n check always causes -1 to be returned).

Probably the manpage should just be modified to say something like "(The value
in *n is ignored on entry, but *n must still point to a valid int, and its value
is updated on exit to reflect the size of the newly malloc'd buffer.)"

This is pretty confusing behavior otherwise -- I had to read the source for
getline() to know what was going on.

Thanks!

-- 
           Summary: Error in getline(3) manpage
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
        AssignedTo: drepper at redhat dot com
        ReportedBy: luke dot hutch at mit dot edu
                CC: glibc-bugs at sources dot redhat dot com


http://sourceware.org/bugzilla/show_bug.cgi?id=5468

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[Bug libc/5468] Error in getline(3) manpage

[drepper at redhat dot com]

------- Additional Comments From drepper at redhat dot com  2007-12-10 22:52 -------
glibc does not come with man pages.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |WONTFIX


http://sourceware.org/bugzilla/show_bug.cgi?id=5468

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[Bug libc/5468] Error in getline(3) manpage

[mtk.manpages at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=5468

--- Comment #3 from Michael Kerrisk <mtk.manpages at gmail dot com> ---
(In reply to Luke Hutchison from comment #0)
> The getline(3) manpage states:
> 
>        ssize_t getline(char **lineptr, size_t *n, FILE *stream);
>  [...]
>        If  *lineptr  is  NULL,  then getline() will allocate a buffer for
> storing the line, which should be
>        freed by the user program.  (The value in *n is ignored.)
> 
> Based on this description (particularly the part that says the value *n is
> ignored), you should be able to do something like:
> 
>     char *line = NULL;
>     getline(&line, NULL, stream);
> 
> However this always fails, because the code for getline does the following:
> 
>   if (!lineptr || !n || !stream)
>     {
>       errno = EINVAL;
>       return -1;
>     }
> 
>   if (!*lineptr)
>     {
>       *n = MIN_CHUNK;
>       *lineptr = malloc (*n);
>       if (!*lineptr)
> 	{
> 	  errno = ENOMEM;
> 	  return -1;
> 	}
>       *lineptr[0] = '\0';
>     }
> 
> (thus the !n check always causes -1 to be returned).
> 
> Probably the manpage should just be modified to say something like "(The
> value
> in *n is ignored on entry, but *n must still point to a valid int, and its
> value
> is updated on exit to reflect the size of the newly malloc'd buffer.)"
> 
> This is pretty confusing behavior otherwise -- I had to read the source for
> getline() to know what was going on.
> 
> Thanks!

getline(3) text changed to read:

       If  *lineptr  is  set  to NULL and *n is set 0 before the call,
       then getline() will allocate a buffer  for  storing  the  line,
       which should be freed by the user program.

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Subject: [Bug manual/1481] No man pages are part of glibc, DO NOT REPORT MAN PAGE BUGS HERE!
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https://sourceware.org/bugzilla/show_bug.cgi?id\x1481

Ben Elliston <bje at sources dot redhat.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|bje at sources dot redhat.com      |

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[Bug libc/5468] Error in getline(3) manpage

[mtk.manpages at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=5468

Michael Kerrisk <mtk.manpages at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mtk.manpages at gmail dot com
         Resolution|WONTFIX                     |DUPLICATE

--- Comment #2 from Michael Kerrisk <mtk.manpages at gmail dot com> ---


*** This bug has been marked as a duplicate of bug 1481 ***

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