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Date: Wed, 16 Jan 2019 13:25:57 -0600
From: "A. Wilcox" <>
Subject: Re: Minor C99 conformance issue: FILE is an incomplete type

On 01/16/19 13:06, Keith Thompson wrote:
> The musl 1.0.0 manual says that it's intended to conform to C99.
> Both the C99 and C11 standards require FILE to be an object type.
> In C99, incomplete types are not object types.  In C11, the definition
> of "object type" was changed, so now incomplete types are object types.
> (See section C99 and C11 6.2.5, C99 7.19.1, C11 7.21.1.)
> So, in C99 FILE is not permitted to be an incomplete type, but in C11
> it is.  (The section describing type FILE did not change.  I don't
> know whether the authors of the standard actually intended to change
> the requirement.)
> Using musl-gcc, FILE is an incomplete type, so it conforms to C11
> but not to C99.  <stdio.h> could be modified so that, for example,
> it pays attention to the value of __STDC_VERSION__ to decide how to
> define FILE (whether to make struct _IO_FILE visible).
> I do not suggest that this minor non-conformance to C99 is a practical
> problem, or even that it should be fixed, merely that it should
> be noted.

This was noted by our POSIX conformance testing.  There was a discussion
in the #musl IRC about possibly making a fake _IO_FILE to satisfy not
just POSIX but some miscreant glibc apps.  However, I believe it was
decided not to do that.


A. Wilcox (awilfox)
Project Lead, Adélie Linux

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