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CMake:Modules

lastmod 2023-03-02created 2016-04-199 edits

Notes on modules written in CMake script.

Category

CMakeParseArguments

Helps parse CMake-style arguments.

FindProtobuf

Example: 

include(FindProtobuf)
find_package(Protobuf REQUIRED)
include_directories(${PROTOBUF_INCLUDE_DIR})
# ...
target_link_libraries(complex
    ${Boost_FILESYSTEM_LIBRARY}
    ${Boost_SYSTEM_LIBRARY}
    ${PROTOBUF_LIBRARY}
)

FindwxWidgets

Not found wxWidgets in MinGW

If it cannot be found properly in MinGW, check the file paths. Refer to the code below. 

if(WX_ROOT_DIR)
    # Select one default tree inside the already determined wx tree.
    # Prefer static/shared order usually consistent with build
    # settings.
    set(_WX_TOOL "")
    set(_WX_TOOLVER "")
    set(_WX_ARCH "")

    if(MINGW)
        set(_WX_TOOL gcc)
    elseif(MSVC)
        set(_WX_TOOL vc)
        if(MSVC14)
            set(_WX_TOOLVER 140)
        elseif(MSVC12)
            set(_WX_TOOLVER 120)
        elseif(MSVC11)
            set(_WX_TOOLVER 110)
        elseif(MSVC10)
            set(_WX_TOOLVER 100)
        elseif(MSVC90)
            set(_WX_TOOLVER 90)
        endif()
        if(CMAKE_SIZEOF_VOID_P EQUAL 8)
            set(_WX_ARCH _x64)
        endif()
    endif()

    ## ...

    find_path(wxWidgets_LIB_DIR
        NAMES
        msw/wx/setup.h
        mswd/wx/setup.h
        mswu/wx/setup.h
        mswud/wx/setup.h
        mswuniv/wx/setup.h
        mswunivd/wx/setup.h
        mswunivu/wx/setup.h
        mswunivud/wx/setup.h
        PATHS
        ${WX_ROOT_DIR}/lib/${_WX_TOOL}${_WX_TOOLVER}${_WX_ARCH}_dll   # prefer shared
        ${WX_ROOT_DIR}/lib/${_WX_TOOL}${_WX_ARCH}_dll                 # prefer shared
        ${WX_ROOT_DIR}/lib/${_WX_TOOL}${_WX_TOOLVER}${_WX_ARCH}_lib
        ${WX_ROOT_DIR}/lib/${_WX_TOOL}${_WX_ARCH}_lib
        DOC "Path to wxWidgets libraries"
        NO_DEFAULT_PATH)

    ## ...
endif ()

In the end, the wx-base library must be located at a path such as C:\wxWidgets-3.1.0\lib\gcc_dll\libwxbase31u.a.

Also, for MinGW, the order of Components matters. 

# Note that for MinGW users the order of libs is important!
find_package(wxWidgets COMPONENTS net gl core base)

ExternalProject

Applies an external project. It is applied according to the overall build order.

Example

Below is an example that downloads and installs zlib. 

include (ExternalProject)

set (DEP_PREFIX_DIR  "${CMAKE_BINARY_DIR}/dep/source")
set (DEP_INSTALL_DIR "${CMAKE_BINARY_DIR}/dep/local")

ExternalProject_Add (zlib
    PREFIX "${DEP_PREFIX_DIR}"
    #--Download step--------------
    URL "http://www.zlib.net/zlib-1.2.11.tar.gz"
    URL_MD5 "1c9f62f0778697a09d36121ead88e08e"
    #--Configure step-------------
    CMAKE_ARGS "-DCMAKE_MACOSX_RPATH=TRUE"
               "-DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}"
               "-DCMAKE_INSTALL_PREFIX=${DEP_INSTALL_DIR}"
    #--Output logging-------------
    LOG_DOWNLOAD 1
    )

ProcessorCount

You can check the number of processes as follows. 

include (ProcessorCount)
ProcessorCount (_process_count)
message ("process: ${_process_count}")

CMakeParseArguments

As an example here a my_install() macro, which takes similar arguments as the real install() command: 

function(MY_INSTALL)
  set(options OPTIONAL FAST)
  set(oneValueArgs DESTINATION RENAME)
  set(multiValueArgs TARGETS CONFIGURATIONS)
  cmake_parse_arguments(MY_INSTALL "${options}" "${oneValueArgs}" "${multiValueArgs}" ${ARGN} )
  ...

Assume my_install() has been called like this: 

my_install(TARGETS foo bar DESTINATION bin OPTIONAL blub)

After the cmake_parse_arguments() call the macro will have set the following variables: 

MY_INSTALL_OPTIONAL = TRUE
MY_INSTALL_FAST = FALSE (this option was not used when calling my_install()
MY_INSTALL_DESTINATION = "bin"
MY_INSTALL_RENAME = "" (was not used)
MY_INSTALL_TARGETS = "foo;bar"
MY_INSTALL_CONFIGURATIONS = "" (was not used)
MY_INSTALL_UNPARSED_ARGUMENTS = "blub" (no value expected after "OPTIONAL"

You can then continue and process these variables.

GenerateExportHeader

Windows Symbol export

To try this out on an existing project, run 

$ cmake -DCMAKE_WINDOWS_EXPORT_ALL_SYMBOLS=TRUE -DBUILD_SHARED_LIBS=TRUE

on a CMake project. This should turn all add_library calls that do not explicitly specify build type into shared builds. If there are no global data variables in the project, all libraries will be built as DLLs with no errors. If you run into undefined symbols, check for global data like static data members of classes. The easiest way to handle the global data is to use the CMake GenerateExportHeader module like this: 

add_library(mylibrary ${mylibrary_SOURCES})
# add these lines
include(GenerateExportHeader)
generate_export_header(mylibrary)

FindwxWidgets

Find a wxWidgets (a.k.a., wxWindows) installation.

Could NOT find wxWidgets in Windows

If you installed wxWidgets on Windows using MSYS, try applying the following. 

set (wxWidgets_ROOT_DIR "C:\\wxWIdgets")
set (CMAKE_CROSSCOMPILING  YES) # Force setting: wxWidgets_FIND_STYLE = unix

FetchContent

Examples

How to create a module

To search for files, use the following commands.

  • find_file
  • find_library
  • find_package
  • find_path
  • find_program

Then create the cache with the mark_as_advanced command.

author Zer0 sitemap