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X-Authentication-Warning:	slinky.cs.nyu.edu: pechtcha owned process doing -bs
Date:	Tue, 10 Dec 2002 10:36:04 -0500 (EST)
From:	Igor Pechtchanski <pechtcha AT cs DOT nyu DOT edu>
Reply-To:	cygwin AT cygwin DOT com
To:	Noel Gordon <noelg AT blueskyinternet DOT com DOT au>
cc:	cygwin AT cygwin DOT com
Subject:	Re: cygwin 1.3.17-1 gethostbyname() leak
In-Reply-To:	<01a001c2a029$0d9950d0$3492fea9@NOELG>
Message-ID:	<Pine.GSO.4.44.0212101024110.12239-100000@slinky.cs.nyu.edu>
Importance:	Normal
MIME-Version:	1.0

On Tue, 10 Dec 2002, Noel Gordon wrote:

> Anyone else confirm that the following program compiled under
> gcc 3.2, cygwin 1.3.17-1, on Win2k leaks memory?
>
> /*-----------------------------------------------------------*/
>
> #include <netdb.h>
> #include <stdio.h>
>
> int main()
> {
>   struct hostent *host;
>
>   while ( 1 )
>   {
>     if ( ( host = gethostbyname( "localhost" ) ) != NULL )
>       printf( "gethostbyname(): %s\n", host->h_name );
>   }
> }

Noel,

From http://www.opengroup.org/onlinepubs/007904975/functions/gethostbyaddr.html :

      The gethostbyaddr() and gethostbyname() functions *may* return
      pointers to static data, which may be overwritten by subsequent
      calls to any of these functions.

The "may" above (emphasis is mine) means that the implementation is free
to malloc a data structure and require the user to free it.  Since you
don't free the returned data structure in your program, it's quite
possible that there's a leak.  Also, Cygwin uses the gethostbyname from
wsock32.dll, which may have different implementations on different
systems.  Thus, your best bet is to look up gethostbyname on MSDN for
implementation details.
	Igor
-- 
				http://cs.nyu.edu/~pechtcha/
      |\      _,,,---,,_		pechtcha AT cs DOT nyu DOT edu
ZZZzz /,`.-'`'    -.  ;-;;,_		igor AT watson DOT ibm DOT com
     |,4-  ) )-,_. ,\ (  `'-'		Igor Pechtchanski
    '---''(_/--'  `-'\_) fL	a.k.a JaguaR-R-R-r-r-r-.-.-.  Meow!

"Water molecules expand as they grow warmer" (C) Popular Science, Oct'02, p.51


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