c++ - CMake can't detect gcc built-in functions such as sqrt, pow ,exp and so on -

i wanna use cmake detect whether built-in functions of gcc exist. used check_function_exists command checking works. here code snippet in cmakelists.txt.

include (checkfunctionexists) set (cmake_required_includes math.h) set (cmake_required_libraries m) check_function_exists(sqrt have_sqrt) check_function_exists (pow have_pow) check_function_exists (exp have_exp) check_function_exists (log have_log) 

code snippet in tutorialconfig.h.in

// configured options , settings tutorial #define tutorial_version_major @tutorial_version_major@ #define tutorial_version_minor  @tutorial_version_minor@ #cmakedefine use_mymath #cmakedefine have_sqrt #cmakedefine have_pow #cmakedefine have_log #cmakedefine have_exp 

   however, directory when executed cmake command under source directory. got such error, weird.

-- c compiler identification gnu 7.0.0 -- cxx compiler identification gnu 7.0.0 -- check working c compiler: /usr/bin/cc -- check working c compiler: /usr/bin/cc -- works -- detecting c compiler abi info -- detecting c compiler abi info - done -- detecting c compile features -- detecting c compile features - done -- check working cxx compiler: /usr/bin/c++ -- check working cxx compiler: /usr/bin/c++ -- works -- detecting cxx compiler abi info -- detecting cxx compiler abi info - done -- detecting cxx compile features -- detecting cxx compile features - done -- looking sqrt cmake error: source directory "../build/cmakefiles/cmaketmp" not exist. specify --help usage, or press button on cmake gui. cmake error @ /usr/share/cmake/modules/checkfunctionexists.cmake:70 (try_compile):   failed configure test project build system. call stack (most recent call first):   cmakelists.txt:23 (check_function_exists) 

   however, directory claimed in error message indeed exists.

$ ls -la ../build/cmakefiles/cmaketmp    total 0   drwxrwxrwx 1 root root 0 apr 14 21:41 .   drwxrwxrwx 1 root root 0 apr 14 20:32 .. 

   not expert in cmake, can't figure out crux.

   here my log file outputed cmake

hope familiar cmake gives me hand. in advance.

error message

cmake error: source directory "../build/cmakefiles/cmaketmp" not exist. 

is possible if relative path used build directory.

while not explicitely stated in docs (and not checked cmake itself), better use absolute path build directory.

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because build directory of cmake project isn't designed moved other place (or on other machine), there no reason using relative path it.