Re: [Boost-users] xlcpp: use of undeclared identifier 'decltype' used in boost/thread/lockable_traits.hpp

On 9/9/2019 8:58 PM, Roy Musselman via Boost-users wrote:

Greetings,

While attempting to build boost 1.70.0 for IBM Power9 using the IBM XL compilers using the SPACK tool, the following errors occur repeatedly for every header file that eventually includes boost/thread/lockable_traits.hpp

In file included from ./boost/thread/lock_types.hpp:14:

*./boost/thread/lockable_traits.hpp*:157:11: error: use of undeclared identifier 'decltype' decltype(void(boost::declval().lock())) ^ ./boost/thread/lockable_traits.hpp:165:11: error: use of undeclared identifier 'decltype' decltype(void(boost::declval().unlock())) ^ ./boost/thread/lockable_traits.hpp:173:11: error: use of undeclared identifier 'decltype' decltype(bool(boost::declval().try_lock())) ^

These errors could be resolved if the *-std=c++11*compiler option is used. Attempting to use SPACK options *cxxflags=-std=c++11*or *cxxstd=11*failed as if they were ignored. I was able to work-around this pervasive error by adding the following line to the file *tools/build/src/tools/xlcpp.jam*

flags xlcpp.compile.c++ OPTIONS <cxxstd>11 : -std=c++11 ;

Can you update the xlcpp.jam file to support the cxxstd=11 option, similar to what is implemented in pgi.jam?

I do not know why cxxflags=-std=c++11 did not work. Maybe it needed to be surrounded by quotes for whatever OS script you are using. Do you have a list of all the possible -std= choices for the compiler ? If we include one for c++11 we should probably include one for each possible choice.