The CXX compiler identification is unknown: xcode

Question

I am trying to install an external library into my C++ project using Cmake. I want the Xcode project to be produced with that library. In my terminal i run the following from the build directory:

cmake -G Xcode ..

and that gives me the following errors:

-- The CXX compiler identification is unknown
-- The C compiler identification is unknown
CMake Error at CMakeLists.txt:6 (project):
No CMAKE_CXX_COMPILER could be found.

CMake Error at CMakeLists.txt:6 (project):
  No CMAKE_C_COMPILER could be found.

I am using g++ compiler:

 Configured with: --prefix=/Library/Developer/CommandLineTools/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
    Apple LLVM version 7.0.0 (clang-700.1.76)
    Target: x86_64-apple-darwin14.5.0
    Thread model: posix

Edit: CMakeLists.txt file

file(READ "${CMAKE_CURRENT_SOURCE_DIR}/VERSION" PROJECT_VERSION_FULL)
string(REGEX REPLACE "[\n\r]" "" PROJECT_VERSION_FULL "${PROJECT_VERSION_FULL}")
string(REGEX REPLACE "^([0-9]+)\\.[0-9]+\\.[0-9]+$" "\\1" PROJECT_VERSION_MAJOR "${PROJECT_VERSION_FULL}")
string(REGEX REPLACE "^[0-9]+\\.([0-9]+)\\.[0-9]+$" "\\1" PROJECT_VERSION_MINOR "${PROJECT_VERSION_FULL}")
string(REGEX REPLACE "^[0-9]+\\.[0-9]+\\.([0-9]+)$" "\\1" PROJECT_VERSION_PATCH "${PROJECT_VERSION_FULL}")
set(PROJECT_VERSION "${PROJECT_VERSION_MAJOR}.${PROJECT_VERSION_MINOR}")
math(EXPR LIBRARY_VERSION_MAJOR "${PROJECT_VERSION_MAJOR}")
set(LIBRARY_VERSION_MINOR "${PROJECT_VERSION_MINOR}")
set(LIBRARY_VERSION_PATCH "${PROJECT_VERSION_PATCH}")
set(LIBRARY_VERSION "${LIBRARY_VERSION_MAJOR}.${LIBRARY_VERSION_MINOR}")
set(LIBRARY_VERSION_FULL "${LIBRARY_VERSION}.${LIBRARY_VERSION_PATCH}")


option(CODE_COVERAGE "Set ON to add code coverage compile options" OFF)
option(GENERATE_DOC "Set ON to genrate doxygen API reference in build/doc directory" OFF)

# C++11 compiler Check
if(NOT CMAKE_CXX_COMPILER_VERSION) # work around for cmake versions smaller than 2.8.10
    execute_process(COMMAND ${CMAKE_CXX_COMPILER} -dumpversion OUTPUT_VARIABLE CMAKE_CXX_COMPILER_VERSION)
endif()
if(CMAKE_CXX_COMPILER MATCHES ".*clang" OR CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
      set(CMAKE_COMPILER_IS_CLANGXX 1)
endif()
if( (CMAKE_COMPILER_IS_GNUCXX AND ${CMAKE_CXX_COMPILER_VERSION} VERSION_LESS 4.7) OR
    (CMAKE_COMPILER_IS_CLANGXX AND ${CMAKE_CXX_COMPILER_VERSION} VERSION_LESS 3.2))
  message(FATAL_ERROR "Your C++ compiler does not support C++11. Please install g++ 4.7 (or greater) or clang 3.2 (or greater)")
else()
  message(STATUS "Compiler is recent enough to support C++11.")
endif()

if( CMAKE_COMPILER_IS_GNUCXX )
    append_cxx_compiler_flags("-std=c++11 -Wall -Wextra  -DNDEBUG" "GCC" CMAKE_CXX_FLAGS)
    append_cxx_compiler_flags("-O3 -ffast-math -funroll-loops" "GCC" CMAKE_CXX_OPT_FLAGS)
    if ( CODE_COVERAGE )
        append_cxx_compiler_flags("-g -fprofile-arcs -ftest-coverage -lgcov" "GCC" CMAKE_CXX_FLAGS)
    endif()

else()
    if(MSVC)
        append_cxx_compiler_flags("/EHsc" "MSVC" CMAKE_CXX_FLAGS)
        append_cxx_compiler_flags("/Od" "MSVC" CMAKE_CXX_FLAGS_DEBUG)
        append_cxx_compiler_flags("/Ox" "MSVC" CMAKE_CXX_FLAGS_RELEASE)
        set(vars CMAKE_CXX_FLAGS CMAKE_CXX_FLAGS_DEBUG CMAKE_CXX_FLAGS_RELEASE CMAKE_CXX_FLAGS_MINSIZEREL CMAKE_CXX_FLAGS_RELWITHDEBINFO)
        foreach(var ${vars})
            string(REPLACE "/MD" "-MT" ${var} "${${var}}")
        endforeach(var)

        add_definitions("/DMSVC_COMPILER")
    else()
        append_cxx_compiler_flags("-std=c++11 -DNDEBUG" "CLANG" CMAKE_CXX_FLAGS)
        append_cxx_compiler_flags("-stdlib=libc++" "CLANG" CMAKE_CXX_FLAGS)
        append_cxx_compiler_flags("-O3 -ffast-math -funroll-loops" "CLANG" CMAKE_CXX_OPT_FLAGS)
    endif()
endif()

Also CMakeEdit.log:

Compiling the CXX compiler identification source file "CMakeCXXCompilerId.cpp" failed.
Compiler:  
Build flags: 
Id flags: 

The output was:
1
xcode-select: error: tool 'xcodebuild' requires Xcode, but active developer directory '/Library/Developer/CommandLineTools' is a command line tools instance


Compiling the C compiler identification source file "CMakeCCompilerId.c" failed.
Compiler:  
Build flags: 
Id flags: 

The output was:
1
xcode-select: error: tool 'xcodebuild' requires Xcode, but active developer directory '/Library/Developer/CommandLineTools' is a command line tools instance

EDIT:

This problem happens when xcode-select developer directory was pointing to /Library/Developer/CommandLineTools, when a full regular XCode was required (happens when CLT are installed after XCode).

I have found the solution to be this:

sudo xcode-select -s /Applications/Xcode.app/Contents/Developer

After this being done, when I run cmake -G Xcode .. I get other errors:

-- The CXX compiler identification is AppleClang 7.0.0.7000176
-- The C compiler identification is AppleClang 7.0.0.7000176
CMake Error at /usr/local/Cellar/cmake/3.4.0/share/cmake/Modules/Platform/Darwin.cmake:76 (message):
  CMAKE_OSX_DEPLOYMENT_TARGET is '10.10' but CMAKE_OSX_SYSROOT:

   ""

  is not set to a MacOSX SDK with a recognized version.  Either set
  CMAKE_OSX_SYSROOT to a valid SDK or set CMAKE_OSX_DEPLOYMENT_TARGET to
  empty.
Call Stack (most recent call first):
  /usr/local/Cellar/cmake/3.4.0/share/cmake/Modules/CMakeSystemSpecificInformation.cmake:36 (include)
  CMakeLists.txt:6 (project)

EDIT 2 Looks like the SDK specified by the OS is wrong.

CMAKE_OSX_DEPLOYMENT_TARGET is '10.10' but the matching SDK does not exist
  at:

   "/Applications/DEV/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.10.sdk"

  Instead using SDK:

   "/Applications/DEV/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.11.sdk".
Call Stack (most recent call first):
  /usr/local/Cellar/cmake/3.4.0/share/cmake/Modules/CMakeSystemSpecificInitialize.cmake:18 (include)
  CMakeLists.txt:6 (project)


-- The CXX compiler identification is AppleClang 7.0.0.7000176
-- The C compiler identification is AppleClang 7.0.0.7000176
CMake Error at /usr/local/Cellar/cmake/3.4.0/share/cmake/Modules/Platform/Darwin.cmake:76 (message):
  CMAKE_OSX_DEPLOYMENT_TARGET is '10.10' but CMAKE_OSX_SYSROOT:

   ""

  is not set to a MacOSX SDK with a recognized version.  Either set
  CMAKE_OSX_SYSROOT to a valid SDK or set CMAKE_OSX_DEPLOYMENT_TARGET to
  empty.
Call Stack (most recent call first):
  /usr/local/Cellar/cmake/3.4.0/share/cmake/Modules/CMakeSystemSpecificInformation.cmake:36 (include)
  CMakeLists.txt:6 (project)

Answer 1

I had the same problem, but I solved it with:

sudo xcode-select --reset

Before doing the above, xcode-select -p reported the path was /Library/Developer/CommandLineTools.

After the reset, the path was /Applications/Xcode.app/Contents/Developer.

Answer 2

I had the same output and could solve it by agreeing to the apple license.

sudo xcodebuild -license accept

Answer 3

The error you have with the SDK can usually be solved by clearing the CMake build cache and adding the following to your CMakeLists.txt before project():

SET(MACOSX_DEPLOYMENT_TARGET ${DARWIN_MAJOR_SDK_VERSION}.${DARWIN_MINOR_SDK_VERSION})
SET(CMAKE_CXX_FLAGS "--sysroot ${CMAKE_OSX_SYSROOT} ${CMAKE_CXX_FLAGS}")
MESSAGE("Setting MACOSX_DEPLOYMENT_TARGET to '${MACOSX_DEPLOYMENT_TARGET}'.")

If you find that doesn't solve the issue then you should check the version of Xcode is current and has the SDK installed you are specifying. Generally Homebrew and Macports CMake both should have the latest stable build of Xcode installed.

↳ https://github.com/Homebrew/homebrew/issues/23074

Answer 4

I had the same issue and as mentioned in one of the comments it appears to be due to the fact that I installed the command-line tools first.

I solved it by opening the Xcode app, going to Preferences -> Locations, and selecting the Xcode installation from the dropdown for Command Line Tools. It was initially blank.