On Fri, Jan 16, 2004 at 05:23:01PM -0800, Tim Kientzle wrote: > I've been enabling a LOT of gcc warnings recently > in the process of linting some code I'm writing. > In the process, I stumbled across the following > curiosity: > > > cat test.c > #include <stdio.h> > > gcc -std=c99 -ansi test.c > In file included from test.c:1: > /usr/include/stdio.h:220: conflicting types for `restrict' > /usr/include/stdio.h:220: previous declaration of `restrict' > /usr/include/stdio.h:221: conflicting types for `restrict' > /usr/include/stdio.h:221: previous declaration of `restrict' > /usr/include/stdio.h:222: redefinition of `restrict' > /usr/include/stdio.h:222: `restrict' previously declared here > /usr/include/stdio.h:223: conflicting types for `restrict' > [ .... many similar lines omitted .... ] > > If I change all "__restrict" in stdio.h to "__restrict__", > these warnings disappear. > > Question: Does anyone know the difference between > __restrict and __restrict__? > __restrict__ is the gcc(1)-only feature. From gcc.info:
: `-std=' : Determine the language standard. This option is currently only : supported when compiling C or C++. A value for this option must be : provided; possible values are : [...] : Even when this option is not specified, you can still use some of : the features of newer standards in so far as they do not conflict : with previous C standards. For example, you may use : `__restrict__' even when `-std=c99' is not specified. : [...] : As with gcc, g++ understands the C99 feature of restricted pointers, : specified with the `__restrict__', or `__restrict' type qualifier. : Because you cannot compile C++ by specifying the `-std=c99' language : flag, `restrict' is not a keyword in C++. __restrict is defined in <sys/cdefs.h>, it's the FreeBSD feature. > Should we be using the latter in our system headers? > No, we should be using the __restrict as coded. But I wonder why we can't just use "restrict", please see below. Note that __restrict is a no-op these days because we don't compile our C code by default with -std=c99. I'm not sure why we can't replace #if !(__GNUC__ == 2 && __GNUC_MINOR__ == 95) #if !defined(__STDC_VERSION__) || __STDC_VERSION__ < 199901 #define __restrict #else #define __restrict restrict #endif #endif with #if !defined(__STDC_VERSION__) || __STDC_VERSION__ < 199901 #define restrict #endif and just use "restrict" everywhere. Also similarly I'm not aware of the status of the CSTD feature for share/mk that was backed out. (8 makefiles in src/ still have CSTD.) Cheers, -- Ruslan Ermilov FreeBSD committer [EMAIL PROTECTED]
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