Be wary of “Boost”, not “boost” in CMakeLists.txt

In Cygwin, the following statements in CMakeLists.txt:

......
find_package(boost 1.66 REQUIRED COMPONENTS system)
if(Boost_FOUND)
    include_directories(${Boost_INCLUDE_DIRS})
    add_executable(play main.cpp)
    target_link_libraries(play ${Boost_LIBRARIES})
endif()
......

causes following errors:

......
CMakeFiles/play.dir/main.cpp.o: In function `boost::system::error_code::error_code()':
/usr/include/boost/system/error_code.hpp:449: undefined reference to `boost::system::system_category()'
/usr/include/boost/system/error_code.hpp:449:(.text$_ZN5boost6system10error_codeC1Ev[_ZN5boost6system10error_codeC1Ev]+0x17): relocation truncated to fit: R_X86_64_PC32 against undefined symbol `boost::system::system_category()'
CMakeFiles/play.dir/main.cpp.o: In function `boost::system::error_category::std_category::equivalent(int, std::error_condition const&) const':
/usr/include/boost/system/error_code.hpp:676: undefined reference to `boost::system::generic_category()'
/usr/include/boost/system/error_code.hpp:676:(.text$_ZNK5boost6system14error_category12std_category10equivalentEiRKSt15error_condition[_ZNK5boost6system14error_category12std_category10equivalentEiRKSt15error_condition]+0xa9): relocation truncated to fit: R_X86_64_PC32 against undefined symbol `boost::system::generic_category()'
/usr/include/boost/system/error_code.hpp:679: undefined reference to `boost::system::generic_category()'
/usr/include/boost/system/error_code.hpp:679:(.text$_ZNK5boost6system14error_category12std_category10equivalentEiRKSt15error_condition[_ZNK5boost6system14error_category12std_category10equivalentEiRKSt15error_condition]+0xe4): relocation truncated to fit: R_X86_64_PC32 against undefined symbol `boost::system::generic_category()'
CMakeFiles/play.dir/main.cpp.o: In function `boost::system::error_category::std_category::equivalent(std::error_code const&, int) const':
/usr/include/boost/system/error_code.hpp:706: undefined reference to `boost::system::generic_category()'
/usr/include/boost/system/error_code.hpp:706:(.text$_ZNK5boost6system14error_category12std_category10equivalentERKSt10error_codei[_ZNK5boost6system14error_category12std_category10equivalentERKSt10error_codei]+0xab): relocation truncated to fit: R_X86_64_PC32 against undefined symbol `boost::system::generic_category()'
/usr/include/boost/system/error_code.hpp:709: undefined reference to `boost::system::generic_category()'
/usr/include/boost/system/error_code.hpp:709:(.text$_ZNK5boost6system14error_category12std_category10equivalentERKSt10error_codei[_ZNK5boost6system14error_category12std_category10equivalentERKSt10error_codei]+0xe6): relocation truncated to fit: R_X86_64_PC32 against undefined symbol `boost::system::generic_category()'
/usr/include/boost/system/error_code.hpp:721: undefined reference to `boost::system::generic_category()'
/usr/include/boost/system/error_code.hpp:721:(.text$_ZNK5boost6system14error_category12std_category10equivalentERKSt10error_codei[_ZNK5boost6system14error_category12std_category10equivalentERKSt10error_codei]+0x1be): relocation truncated to fit: R_X86_64_PC32 against undefined symbol `boost::system::generic_category()'
CMakeFiles/play.dir/main.cpp.o: In function `boost::asio::error::get_system_category()':
/usr/include/boost/asio/error.hpp:229: undefined reference to `boost::system::system_category()'
/usr/include/boost/asio/error.hpp:229:(.text$_ZN5boost4asio5error19get_system_categoryEv[_ZN5boost4asio5error19get_system_categoryEv]+0x9): relocation truncated to fit: R_X86_64_PC32 against undefined symbol `boost::system::system_category()'
collect2: error: ld returned 1 exit status

Change boost to Boost:

find_package(Boost 1.66 REQUIRED COMPONENTS system)
......

All is OK now!