CMake complains “The CXX compiler identification is unknown”

I am following this thread and this one to build my own KDE without a sudo permission. Since there was no Git and CMake installed on the workstation. I just had them both installed under /home/< user> and added /home/< user>/bin and /home/< user>/lib to both PATH and LD_LIBRARY_PATH. Since KDE build only supports CMake, not configure. So I have to set the prefix via CMake, like this: cmake ~/kde-devel/src/kdelibs -DCMAKE_INSTALL_PREFIX=/home/<user>. At this point I got below error:

> ~/bin/cmake ~/kde-devel/src/kdelibs -DCMAKE_INSTALL_PREFIX=/home/<user>
-- The CXX compiler identification is unknown
-- Check for working CXX compiler: /home/gnu/bin/c++
-- Check for working CXX compiler: /home/gnu/bin/c++ -- broken
CMake Error at /home/<user>/share/cmake-2.8/Modules/CMakeTestCXXCompiler.cmake:45 (MESSAGE):
  The C++ compiler "/home/gnu/bin/c++" is not able to compile a simple test
  program.

  It fails with the following output:

   Change Dir: /home/<user>/kde-devel/build/kdelibs/CMakeFiles/CMakeTmp



  Run Build Command:/usr/bin/gmake "cmTryCompileExec/fast"
  ...

I checked that there are 2 C++ compilers:

> where c++
/home/gnu/bin/c++
/usr/bin/c++

Should I set CMake default C++ compiler to /usr/bin/c++? and how? Or is there any way to fix this issue?

Answer

Your /home/gnu/bin/c++ seem to require additional flag to link things properly and CMake doesn’t know about that.

To use /usr/bin/c++ as your compiler run cmake with -DCMAKE_CXX_COMPILER=/usr/bin/c++.

Also, CMAKE_PREFIX_PATH variable sets destination dir where your project’ files should be installed. It has nothing to do with CMake installation prefix and CMake itself already know this.