c++ - CMake on Windows

Question

I am trying to run CMake on Windows, and I get the following error:

-- The C compiler identification is unknown
CMake Error at CMakeLists.txt:3 (PROJECT):
  The CMAKE_C_COMPILER:

    cl

  is not a full path and was not found in the PATH.

  To use the NMake generator with Visual C++, cmake must be run from a shell
  that can use the compiler cl from the command line.  This environment is
  unable to invoke the cl compiler.  To fix this problem, run cmake from the
  Visual Studio Command Prompt (vcvarsall.bat).

  Tell CMake where to find the compiler by setting either the environment
  variable "CC" or the CMake cache entry CMAKE_C_COMPILER to the full path to
  the compiler, or to the compiler name if it is in the PATH.

However my "CC" environment variable is set!

>>echo %CC%
C:Anaconda2MinGWx86_64-w64-mingw32ingcc.exe

Answer 1

Because CMake's error message is misleading here, I think it warrants a little more detailed answer.

In short, you ran into a chicken-and-egg kind of a problem.

CMake's compiler detection is mighty, but since - during the first try -

• you didn't give any explicit generator to use with -G
• it couldn't find a Visual Studio installed
• it couldn't find any C/C++ compiler in your PATH environment
• it couldn't find a CC environment variable defined with the full path to a compiler

It was defaulting to nmake.

Now here comes the problem: it does remember your implicit generator/compiler choice in it's variable cache (see CMAKE_GENERATOR in CMakeCache.txt). What is a very useful feature, if you have multiple compilers installed.

But if you then declare the CC environment variable - as the error message suggests - it's too late since your generator's choice was remembered in the first try.

I see two possible ways out of this:

1. Overrule the generator choice by given the right one with cmake.exe -G "MinGW Makefiles" .. (as the answer linked by @Guillaume suggests)
2. Delete your project's binary output directory (including CMakeCache.txt) and do cmake.exe .. after you added your compiler's bin folder to your PATH environment.

References

• Running CMake on Windows
• What is the default generator for CMake in Windows?
• CMake error at CMakeLists.txt:30 (project): No CMAKE_C_COMPILER could be found
• CMake: how to specify the version of Visual C++ to work with?