Vladislav Lesin added a comment - 2019-11-19 08:41 - edited On some platforms(like Ubuntu 16.04) math.h contains isnan/isinf definition only for C99 standard. If some code is compiled with C++11 standard, math.h does not contain isnan/isinf definitions, it's supposed cmath header and std::isnan, std::isinf, std::isfinite must be used instead of math.h for C++11. Note CHECK_SYMBOL_EXISTS(isnan math.h HAVE_ISNAN) returns true because it uses try_compile() cmake function, which does not apply CMAKE_CXX_FLAGS or CMAKE_CXX_STANDARD in cmake <= 3.7(default cmake version for Ubuntu 16.04 is 3.5), and the code, passed as an argument to try_compile(), is compiled under default C99 standard(if the correspondent compilation flag is not set explicitly in CMAKE_REQUIRED_FLAGS). So if we use CHECK_SYMBOL_EXISTS(...) on Ubuntu 16.04 we have HAVE_ISNAN/HAVE_ISINF set to true, but isnan/isinf are not defined in math.h if the code is compiled under C++11 standard, what is true for ES and 10.4+ CS. To use std::isnan/std::isinf we must include cmath. It was included in my_global.h only if "isfinite" macro is not defined and C++11 is used. But there is another issue. On some platforms like MacOS X, "isfinite" is defined for both C99 and C++11 standards, so on MacOS X cmath was not included in my_global.h, what caused compilation errors for the code which used std::inan/std::isinf/std::isfinite. Besides "isfinite" is deprecated since MacOS 10.9, what led to a lot of warnings during compilation. That is why we include cmath and use std::isfinite on C++11 standard, even if "isfinite" is defined. The solution is to use std::isnan/std::isinf/std::isfinite if the code is compiled with C++11 standard. The corresponding changes were already done for 10.3 CS: commit 7ffd7fe9627d1f750a3712aebb4503e5ae8aea8e Author: Sergey Vojtovich <svoj@mariadb.org> Date: Fri May 25 22:16:04 2018 +0400 Cleanup isnan() portability checks   commit bc469a0bdf85400f7a63834f5b7af1a513dcdec9 Author: Sergey Vojtovich <svoj@mariadb.org> Date: Fri May 25 22:09:07 2018 +0400 Cleanup isinf() portability checks Original problem reported by Wlad: re-compilation of 10.3 on top of 10.2 build would cache undefined HAVE_ISINF from 10.2, whereas it is expected to be 1 in 10.3. std::isinf() seem to be available on all supported platforms.   commit 54999f4e75f42baca484ae436b382ca8817df1dd Author: Sergey Vojtovich <svoj@mariadb.org> Date: Wed May 23 18:52:55 2018 +0400 Use std::isfinite in C++ code This is addition to parent revision fixing build failures.