Re: Building CVS HEAD libtool outside of source directory

[Eric Blake]

Bob Friesenhahn <bfriesen <at> simple.dallas.tx.us> writes:

> > There is a known bug in m4 1.4.10 on platforms where fopen(..., "a+")
> > opens at the tail of a file, rather than the head.  It looks like this is
> > what is biting you.

The bug is already fixed in M4 CVS; using the patch from the referenced mail.

> 
> Facinating.  I would expect opening for append to open at the tail 
> (end) of the file although I find your use of 'head' and 'tail' to be 
> confusing since a file is not a queue.

POSIX says the state of the first ftell() on a file after fopen("a+") is
implementation-defined - it can be either offset 0 (as glibc) or the end of the
file (as on BSD).  It isn't until you do either an explicit seek (which is what
my m4 patch adds) or a write that the position is then well-defined.

> It sounds like your code is fighting against the intentions of "a+" 
> and that the seek in your referenced patch will be ignored by FreeBSD 
> and OS X and should probably be ignored by Solaris as well.

No, no problem with my code, once I added the requisite seek.

> 
> Maybe freopen() can help?

Not necessary here.  If fopen()/fseek() can't solve the problem, freopen() won't
help either.

-- 
Eric Blake