C++11 narrowing problem in gil

[Jim Bosch]

Compiling against Boost.Gil on Clang with C++11 extensions enabled, I get an error about narrowing in channel_algorithms.hpp. The attached patch fixes the problem and works fine with C++03 as well.

The clang version is compiled from svn, running on Ubuntu 10.04: clang version 3.2 (trunk 162287) Target: x86_64-unknown-linux-gnu Thread model: posix

[Jim Bosch]

updated patch that avoids introducing a new problem

[Jim Bosch]

Looking closer, my original patch would solve the problem but probably create some new ones, by always casting to unsigned int instead of the template parameter type. I've now attached a new patch that avoids mistake.

It also looks like one of the partial specializations of the template in the same area could cause problems for C++11, depending on the types it was instantiated with. I'll leave fixing that up to someone more familiar with its purpose.

[chhenning]

This has been fixed. See ticket 7970

[babatakao@…]

boost 1.61 still causes the error with clang: Apple LLVM version 7.3.0 (clang-703.0.31)

/buildroot/libs/boost/include/boost/gil/channel_algorithm.hpp:55:85: error: non-type template argument evaluates to -1, which cannot be narrowed to type 'unsigned long' [-Wc++11-narrowing]
struct unsigned_integral_max_value : public mpl::integral_c<UnsignedIntegralChannel,-1> {};
                                                                                    ^
/buildroot/libs/boost/include/boost/gil/channel_algorithm.hpp:55:85: /libs/boost/include/boost/gil/channel_algorithm.hpp:205:19: note: in instantiation of template class 'boost::gil::detail::unsigned_integral_max_value<unsigned long>' requested here
        if (src > unsigned_integral_max_value<uintmax_t>::value - div2)
                  ^
1 error generated.

and it does not seem to be fixed on boost 1.63.0 beta1.

(The error occurs only if "-std=c++11" is given.)

"boost-gil-clang-c++11-narrowing.patch" fixes the error.

[Mateusz Loskot]

This should have been fixed by ​https://github.com/boostorg/gil/commit/e3cba43c16e1958e8dac1ca9cb5745d9d6a68068 (Feb 6, 2013)