CMake can't find GLEW

I've read this [1], but in my case CMake says it can't find glew.

I'm on Windows and there is a FindGLEW.cmake file in my CMake modules folder, presumably put there when I installed CMake-3.6. I found GLEW on sourceforge and downloaded the zip file for Windows. I unzipped and installed in C:\Program Files\glew. When I've created my own libraries and used CMake to build and install them, this is the default location they are installed to so I am pretty confident I'm OK here.

The snippet from my CMakeLists.txt is:

find_package(GLEW REQUIRED)
include_directories(${GLEW_INCLUDE_DIRS})
link_libraries(${GLEW_LIBRARIES})

The actual error message from CMake is:

CMake Error at C:/Program Files/CMake/share/cmake-3.6/Modules/FindPackageHandleStandardArgs.cmake:148 (message):
  Could NOT find GLEW (missing: GLEW_INCLUDE_DIR GLEW_LIBRARY)
Call Stack (most recent call first):
  C:/Program Files/CMake/share/cmake-3.6/Modules/FindPackageHandleStandardArgs.cmake:388 (_FPHSA_FAILURE_MESSAGE)
  C:/Program Files/CMake/share/cmake-3.6/Modules/FindGLEW.cmake:44 (find_package_handle_standard_args)
  source/CMakeLists.txt:5 (find_package)

Is it possible the FindGLEW.cmake is broken? I've looked at a couple of other FindXXXXX.cmake files and they are like snowflakes, each one pretty unique. So it's hard for me to say with any certainty that it's following convention.

[1] Linking GLEW with CMake

Solution

Looking in the sources, the package is looking for GLEW in relative paths. These relative paths are searched using different prefixes, including the content of the variable CMAKE_PREFIX_PATH:

<prefix>/include for find_path which is used to find include directories.
<prefix>/lib for find_library which is used to find libraries.

Assuming C:/Program Files/glew/include and C:/Program Files/glew/lib exist, add C:/Program Files/glew to your CMAKE_PREFIX_PATH variable. Something like:

list(APPEND CMAKE_PREFIX_PATH "C:/Program Files/glew")
find_package(GLEW REQUIRED)

Note that the following lines:

include_directories(${GLEW_INCLUDE_DIRS})
link_libraries(${GLEW_LIBRARIES})

may be dropped using imported target Glew::Glew:

add_executable(foo ...)
target_link_libraries(foo Glew::Glew)