Date: Tue, 7 Nov 2000 12:17:34 +0200 From: Peter Pentchev <roam@orbitel.bg> To: Giorgos Keramidas <keramida@ceid.upatras.gr> Cc: hackers@freebsd.org Subject: Re: umask(2) and -Wconversion Message-ID: <20001107121734.D314@ringworld.oblivion.bg> In-Reply-To: <20001107120511.A98074@gray.westgate.gr>; from keramida@ceid.upatras.gr on Tue, Nov 07, 2000 at 12:05:11PM %2B0200 References: <20001107120511.A98074@gray.westgate.gr>
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In my experience, the problem is not only with umask(2) - GCC *is*
a bit stubborn about -Wconversion; I wonder if this is really a GCC bug :(
I'm having the same problems with many other functions when passing
integer constants - even if I explicitly cast them to a long or unsigned
long or plain unsigned int or whatever the particular function needs,
GCC seems to ignore the cast and whines about the conversion nonetheless :(
Can anybody else confirm this? I can't dig out a code snippet right now,
but ISTR a recurring case of this when compiling with BDECFLAGS a program
which includes ncurses.h, then passes integer constants to init_pair()
or something similar.
G'luck,
Peter
--
If there were no counterfactuals, this sentence would not have been paradoxical.
On Tue, Nov 07, 2000 at 12:05:11PM +0200, Giorgos Keramidas wrote:
> While trying to compile libskey with various warnings enabled, I
> discovered the following funny thing about -Wconversion and umask(2),
> which caused libskey to fail to compile, because it compiles by default
> with -Werror which makes every warning fatal.
>
> I found that the warning is caused when a program that calls umask(2) is
> compiled with -Wconversion. The info page of gcc says about -Wconversion:
>
> `-Wconversion'
> Warn if a prototype causes a type conversion that is different
> from what would happen to the same argument in the absence of a
> prototype. This includes conversions of fixed point to floating
> and vice versa, and conversions changing the width or signedness
> of a fixed point argument except when the same as the default
> promotion.
>
> Also, warn if a negative integer constant expression is implicitly
> converted to an unsigned type. For example, warn about the
> assignment `x = -1' if `x' is unsigned. But do not warn about
> explicit casts like `(unsigned) -1'.
>
> The following test program when compiled with -Wconversion shown below
> will always give a warning, even if I explicitly try to cast the
> argument of umask() to mode_t.
>
> 1 #include <stdio.h>
> 2 #include <sys/stat.h>
> 3
> 4 int main (void)
> 5 {
> 6 mode_t oldmask;
> 7
> 8 oldmask = umask(0);
> 9 printf("The umask has changed\n");
> 10 umask(oldmask);
> 11 return 0;
> 12 }
>
> The output given when I compile this with -Wconversion is:
>
> gray-charon:/home/charon/test% gcc -Wconversion test.c -o test
> test.c: In function `main':
> test.c:8: warning: passing arg 1 of `umask' with different width due to prototype
> test.c:10: warning: passing arg 1 of `umask' with different width due to prototype
>
> The problem is that even if I change line 8 to read:
>
> 8 oldmask = umask((mode_t) 0);
>
> the warning is still there. Am I being a bit too strict with all these
> warnings here? If not, does anyone else have any idea why umask(2) will
> always cause such a warning, and how I can go about correcting it?
> Casting obviously fails, so something else needs to be done.
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