CMAKE_COMPILER_IS_GNUCXX and CMAKE_CXX_COMPILER_ID are empty

Question

I am currently playing around with CMake and want to detect the compiler and the compiler version. My current CMakeLists.txt looks as follows:

cmake         


        

Answer 1

It might help you tell CMake that this is a C++ project. To do it you say it in the project command:

project ($(PROJECT) CXX)
#                   ^^^
# Note project type

You might also want to do it before checking the variable.

Answer 2

Place it after project command:

> cat CMakeLists.txt 
cmake_minimum_required(VERSION 2.8)

message("before:")
message(">    ${CMAKE_CXX_COMPILER}")
message(">    ${CMAKE_CXX_COMPILER_ID}")
message(">    ${CMAKE_COMPILER_IS_GNUCXX}")
message("-----------------")

project(Foo)

message("after:")
message(">    ${CMAKE_CXX_COMPILER}")
message(">    ${CMAKE_CXX_COMPILER_ID}")
message(">    ${CMAKE_COMPILER_IS_GNUCXX}")
message("-----------------")

> cmake -H. -B_builds
before:
>    
>    
>    
-----------------
-- The C compiler identification is GNU 4.8.1
-- The CXX compiler identification is GNU 4.8.1
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
after:
>    /usr/bin/c++
>    GNU
>    1
-----------------
-- Configuring done
-- Generating done
-- Build files have been written to: /.../_builds