CMake error occurred while installing PX4 compilation environment: Error

This error has always been thought to be cmake is not installed well, reinstall still have errors;

and CMake--version or display the old version, the old version install removed, the version becomes new;

The last occurrence of the following error, not CMake, is Cross_toolchain installation path is not correct, should be installed in the/home/directory, ctrl +h open hidden files,. bashrc file directories should add their own directory, Sourec ~./ BARSHRC Manual Compilation

CMake Error:cmake_c_compiler not set, after the Enablelanguage CMake Error:cmake_cxx_compiler not set, after Enablelanguage
--Configuring incomplete, Errors occurred!