Boost C++ Libraries: Ticket #6118: Uuid random_generator compiles with warnings by GCC

attachment set

Sat, 12 Nov 2011 16:24:31 GMT

attachment → uuidTest.cpp

test program

keywords changed

Sat, 12 Nov 2011 16:27:12 GMT

keywords gcc added

anonymous — Tue, 22 Nov 2011 12:37:42 GMT

What about casting to void the call to fread?

(void) fread(...)

This should suppress the warning without adding the extra cost to check the value returned by fread.

Otherwise, there is a patch that check this value here: http://boost.2283326.n4.nabble.com/PATCH-1-2-Fixed-warning-ignoring-return-value-of-size-t-fread-void-size-t-size-t-FILE-td3145963.html with the disadvantage of adding another warning when suppressing the BOOST_ASSERT.

Andy Tompkins — Sat, 17 Dec 2011 02:07:31 GMT

Please allow me to rephrase.

As it is, one gets the warning that the return value of std::fread is ignored.

If it is changed to:

size_t not_used = std::fread( ... );

then one gets the warning that not_used is an unused variable

but the following will have no warnings?:

(void) fread( ... );

I checked this into trunk (commit 76007). Please let me know if this does indeed suppress all warnings.

Sat, 17 Dec 2011 12:53:57 GMT

Doesn't solve problem. GCC 4.5.2 reports

cc1plus: warnings being treated as errors In file included from /home/vasily/boost_1_47_0/boost/uuid/random_generator.hpp:12:0,

from uuidTest.cpp:1:

/home/vasily/boost_1_47_0/boost/uuid/seed_rng.hpp: In member function ‘void boost::uuids::detail::seed_rng::sha1_random_digest_()’: /home/vasily/boost_1_47_0/boost/uuid/seed_rng.hpp:152:51: error: value computed is not used /home/vasily/boost_1_47_0/boost/uuid/seed_rng.hpp:152:51: error: ignoring return value of ‘size_t fread(void*, size_t, size_t, FILE*)’, declared with attribute warn_unused_result

I am concerned more about second warning on Solaris and AIX.

Andy Tompkins — Tue, 20 Dec 2011 02:06:56 GMT

This random number generator is slow. That is why it is only used to seed a faster random number generator. Therefore I don't believe that the cost of an extra assignment or two will be significant. I checked in the following (trunk commit 76076):

size_t not_used = 0;
not_used = fread( ... );

Does this get rid of all the warnings?

Thu, 05 Jan 2012 09:16:37 GMT

Compilation passes with gcc 4.5, but fails in 4.6

/emc/sukhav/cross/boost_1_47_0/boost/uuid/seed_rng.hpp:152:15: error: variable ‘not_used’ set but not used [-Werror=unused-but-set-variable]

-Wunused-but-set-variable is new warning introduced in 4.6 branch.

Andy Tompkins — Fri, 17 Feb 2012 02:27:02 GMT

Changed

not_used = fread( ... );

not_used += fread( ... );

Does this get rid of all the warnings?

Andy Tompkins — Fri, 17 Feb 2012 02:27:44 GMT

Forgot to add that I checked this into trunk revision 77049.

Mon, 05 Mar 2012 12:02:25 GMT

Looks like you fixed warning on Linux. But you haven't proposed a fix for the second one (AIX/Solaris). At boost/uuid/seed_rng.hpp:244 there is default-initialized generator_iterator. But generator_iterator::generator_iterator() leaves generator_iterator::m_value uninitialized. I reproduced with boost 1.48.

markus@… — Sun, 18 Mar 2012 06:58:21 GMT

Happy it's fixed, but I think a clearer fix would be:

inline void ignore_size(size_t s){} ... ignore_size(std::fread(...));

This won't ever generate instructions or be 'outed' by a compiler as a null operation.

cc set

Fri, 29 Jun 2012 21:10:33 GMT

cc jonathan.jones@… added

benjamin.mahler@… — Tue, 28 Aug 2012 17:14:48 GMT

Any update on fixing the second warning?

end.boost::uuids::detail::generator_iterator<boost::uuids::detail::seed_rng>::m_value' is used uninitialized in this function

Andy Tompkins — Wed, 12 Sep 2012 01:17:48 GMT

I've checked in the ignore_size suggestion in the hopes that it will get rid of all warnings.

I've also checked a fix for the second warning.

Both rev 80501

status changed; resolution set

Andy Tompkins — Thu, 04 Oct 2012 17:09:28 GMT

status new → closed
resolution → fixed

checked in release - changeset #80846