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Date: Mon, 13 Jan 2014 13:09:33 +0100
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: nested popen()'s lead to fgets() failure on 64-bit only
Message-ID: <20140113120933.GA21977@calimero.vinschen.de>
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References: <18833-1389579359 DOT 738859 AT Poig DOT bVYt DOT cj35>
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On Jan 12 21:15, David Levine wrote:
> Hi,
>=20
> The program below works just fine on 32-bit Cygwin:
>   buf1 =3D /usr/bin/file.exe
>   buf2 =3D /usr/bin/file.exe: application/x-dosexec
>=20
> But on 64-bit Cygwin (2.831), the second fgets() fails:

That's the version number of the setup-x86_64.exe tool, not the version
number of Cygwin.  Try `uname -r'.

>   buf1 =3D /usr/bin/file.exe
> fgets2: No error
>=20
> It only seems to happen with nested popen()'s.  Is it due to a
> problem in the Cygwin lib?

Works fine for me on Cygwin 1.7.27:

  $ uname -rm
  1.7.27(0.271/5/3) x86_64
  $ file --version
  file-5.13
  magic file from /usr/share/misc/magic
  $ ./popen-test
    buf1 =3D /usr/bin/file.exe
    buf2 =3D /usr/bin/file.exe: application/x-dosexec
  $

The fact that fgets returns NULL doesn't mean an error occured.  fgets
also returns NULL at EOF, meaning no output in this case, which you
should test, too:

  if (fgets(buf2, sizeof buf2, f2))
    printf("  buf2 =3D %s", buf2);
  else if (feof (f2))
    fputs ("fgets2 EOF\n", stderr);
  else
    perror("fgets2");

Maybe you're calling the wrong file command?  What's your $PATH set to?
What if you change your popen call to run /usr/bin/file.exe with full
path?

  if ((f2 =3D popen("/usr/bin/file --mime-type /usr/bin/file.exe", "r")))


Corinna

--=20
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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