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* Minor C99 conformance issue: FILE is an incomplete type
@ 2019-01-16 19:06 Keith Thompson
  2019-01-16 19:25 ` A. Wilcox
  0 siblings, 1 reply; 6+ messages in thread
From: Keith Thompson @ 2019-01-16 19:06 UTC (permalink / raw)
  To: musl; +Cc: Keith Thompson

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.

$ cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=18.04
DISTRIB_CODENAME=bionic
DISTRIB_DESCRIPTION="Ubuntu 18.04.1 LTS"

$ uname -a
Linux bomb20 4.15.0-42-generic #45-Ubuntu SMP Thu Nov 15 19:32:57 UTC
2018 x86_64 x86_64 x86_64 GNU/Linux

$ dpkg -l musl
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name                                      Version
 Architecture              Description
+++-=========================================-=========================-=========================-=======================================================================================
ii  musl:amd64                                1.1.19-1
 amd64                     standard C library

$ gcc --version
gcc (Ubuntu 7.3.0-27ubuntu1~18.04) 7.3.0
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ cat FILE_bug.c.
#include <stdio.h>
int main(void) {
    printf("sizeof (FILE) = %zu\n", sizeof (FILE));
}

$ musl-gcc -std=c99 -c FILE_bug.c
FILE_bug.c: In function ‘main’:
FILE_bug.c:3:45: error: invalid application of ‘sizeof’ to
incomplete type ‘FILE {aka struct _IO_FILE}’
     printf("sizeof (FILE) = %zu\n", sizeof (FILE));
                                             ^~~~
$ musl-gcc -std=c11 -c FILE_bug.c
FILE_bug.c: In function ‘main’:
FILE_bug.c:3:45: error: invalid application of ‘sizeof’ to
incomplete type ‘FILE {aka struct _IO_FILE}’
     printf("sizeof (FILE) = %zu\n", sizeof (FILE));
                                             ^~~~


^ permalink raw reply	[flat|nested] 6+ messages in thread
end of thread, other threads:[~2019-01-16 20:20 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-01-16 19:06 Minor C99 conformance issue: FILE is an incomplete type Keith Thompson
2019-01-16 19:25 ` A. Wilcox
2019-01-16 19:33   ` Rich Felker
2019-01-16 19:47     ` A. Wilcox
2019-01-16 19:57     ` Szabolcs Nagy
2019-01-16 20:20       ` Rich Felker

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