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Date: Sun, 15 Feb 2026 10:59:42 +0100
To: cygwin AT cygwin DOT com
Subject: Re: BUG: "machine/types.h" not protected by multiple #include
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From: Corinna Vinschen via Cygwin <cygwin AT cygwin DOT com>
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On Feb 14 20:41, Carlo B. via Cygwin wrote:
> Hello,
> while compiling libsrtp2, I got this error:
> 
> /usr/include/machine/types.h:35:8: error: redefinition of ‘struct flock’
>    35 | struct flock {
>       |        ^~~~~
> In file included from /usr/include/sys/types.h:222,
>                  from
> ../gstreamer/subprojects/libsrtp-2.7.0/crypto/include/integers.h:60:
> /usr/include/machine/types.h:35:8: note: originally defined here
>    35 | struct flock {
>       |        ^~~~~
> 
> This happens because into the library there is this code:
> 
> <--- CUT --->
> #ifdef HAVE_SYS_TYPES_H
> #include <sys/types.h>
> #endif
> #ifdef HAVE_MACHINE_TYPES_H
> #include <machine/types.h>
> #endif
> <--- CUT --->
> 
> The first inclusion of "sys/types.h" includes also "machine/types.h"
> and this is ok.
> Next, the second directive includes again "machine/types.h" and here
> it generates the error.

Directly including machine/types.h is wrong.  This is a header meant
to be only included via sys/types.h.  It contains this test at the
start of the file:

#ifndef _SYS_TYPES_H
#error "must be included via <sys/types.h>"
#endif /* !_SYS_TYPES_H */

Check this against the files in /usr/include/bits from GLibc.
Many of those files are not guarded against multiple inclusions
either.

Yes, we could guard machine/types.h against multiple inclusion,
but the right thing to do would be to change the above code to
never include machine/types.h.

And if you really think you can't do without, add an #else at least:

  #ifdef HAVE_SYS_TYPES_H
  #include <sys/types.h>
  #elif defined(HAVE_MACHINE_TYPES_H)
  #include <machine/types.h>
  #endif


Corinna

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