title: Cmake error: Could NOT find Boost (missing: Boost_INCLUDE_DIR)
body: <p>I am new to Cmake and Boost. I am now working on a program using cmake and need help.</p>
  
  <p>System: windows 7<br>
  Cmake version: 3.16.0-rc1<br>
  Boost version: boost_1_71_0. And boost is installed through .exe file.<br>
  Gcc version: 4.8.1(rev5, Built by MinGW-W64 project)<br>
  Visual studio: vs 2015  </p>
  
  <p>When I run <code>cmake ..</code> in <code>build</code> dir, no error occurs. The output is:</p>
  
  <pre><code>The C compiler identification is MSVC 19.0.24215.1
  The CXX compiler identification is MSVC 19.0.24215.1
  Check for working C compiler: C:/Program Files (x86)/Microsoft Visual Studio 14.0/VC/bin/cl.exe
  Check for working C compiler: C:/Program Files (x86)/Microsoft Visual Studio 14.0/VC/bin/cl.exe -- works
  Detecting C compiler ABI info
  Detecting C compiler ABI info - done
  Detecting C compile features
  Detecting C compile features - done
  Check for working CXX compiler: C:/Program Files (x86)/Microsoft Visual Studio 14.0/VC/bin/cl.exe
  Check for working CXX compiler: C:/Program Files (x86)/Microsoft Visual Studio 14.0/VC/bin/cl.exe -- works
  Detecting CXX compiler ABI info
  Detecting CXX compiler ABI info - done
  Detecting CXX compile features
  Detecting CXX compile features - done
  Found Boost: C:/local/boost_1_71_0 (found version "1.71.0")  
  Boost_Found Success!
  Found OpenCV: C:/Users/gph/opencv/binaries (found version "3.4.5") 
  Found OpenCV: C:/Users/gph/opencv/binaries (found version "3.4.5") found components: core highgui imgproc videoio 
  Configuring done
  </code></pre>
  
  <p>But I want to use minGW to compile, so When I rum <code>cmake -G "MinGW Makefiles"</code>, error occured saying "Could NOT find Boost (missing: Boost_INCLUDE_DIR)". The output is:</p>
  
  <pre><code>The C compiler identification is GNU 4.8.1
  The CXX compiler identification is GNU 4.8.1
  Check for working C compiler: C:/MinGW/bin/gcc.exe
  Check for working C compiler: C:/MinGW/bin/gcc.exe -- works
  Detecting C compiler ABI info
  Detecting C compiler ABI info - done
  Detecting C compile features
  Detecting C compile features - done
  Check for working CXX compiler: C:/MinGW/bin/g++.exe
  Check for working CXX compiler: C:/MinGW/bin/g++.exe -- works
  Detecting CXX compiler ABI info
  Detecting CXX compiler ABI info - done
  Detecting CXX compile features
  Detecting CXX compile features - done
  CMake Error at C:/Users/gph/cmake/share/cmake-3.16/Modules/FindPackageHandleStandardArgs.cmake:146 (message):
    Could NOT find Boost (missing: Boost_INCLUDE_DIR)
  Call Stack (most recent call first):
    C:/Users/gph/cmake/share/cmake-3.16/Modules/FindPackageHandleStandardArgs.cmake:393 (_FPHSA_FAILURE_MESSAGE)
    C:/Users/gph/cmake/share/cmake-3.16/Modules/FindBoost.cmake:2162 (find_package_handle_standard_args)
    CMakeLists.txt:34 (find_package)
  
  
  Configuring incomplete, errors occurred!
  See also "C:/Users/gph/Desktop/libvibe++/build/CMakeFiles/CMakeOutput.log".
  </code></pre>
  
  <p>How to solve the error when running <code>cmake -G "MinGW Makefiles"</code>? Thanks guys!</p>