[CMake] cmake picks a compiler

[Dave Yost]

Hi.

In our CMakeLists.txt file we want to force the user to pick a c++ compiler explicitly, something like this:

if (NOT DEFINED CMAKE_CXX_COMPILER)
  set(CMAKE_CXX_COMPILER $ENV{CXX})
  if (NOT DEFINED CMAKE_CXX_COMPILER)
    message(FATAL_ERROR " 
 You must choose your compiler, in one of two ways:
   cmake -DCMAKE_CXX_COMPILER=/path/to/compiler++
   CXX=/path/to/compiler++ cmake")
  endif()
endif()
message("CMAKE_CXX_COMPILER: ${CMAKE_CXX_COMPILER}")

Problem is, CMAKE_CXX_COMPILER is already set because cmake looked around and picked a compiler (which causes a lot of messages to be output before cmake executes the above statements).

Z% CMAKE_CXX_COMPILER=/usr/bin/clang++ cmake ..
-- The CXX compiler identification is GNU 4.9.2
-- Checking whether CXX compiler has -isysroot
-- Checking whether CXX compiler has -isysroot - yes
-- Checking whether CXX compiler supports OSX deployment target flag
-- Checking whether CXX compiler supports OSX deployment target flag - yes
-- Check for working CXX compiler: /opt/local/bin/c++
-- Check for working CXX compiler: /opt/local/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
CMAKE_CXX_COMPILER: /opt/local/bin/c++

I need a command I can put in my CMakeLists.txt file to disable the cmake feature that automatically locates a c++ compiler.

Thanks
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