What use is find package if you need to specify CMAKE MODULE PATH anyway

Question

I m trying to get a cross-plattform build system working using CMake  Now the software has a few dependencies  I compiled them myself and installed them on my system   Some example files which got installed   -- Installing   usr local share SomeLib SomeDir somefile -- Installing   usr local share SomeLib SomeDir someotherfile -- Installing   usr local lib SomeLib somesharedlibrary -- Installing   usr local lib SomeLib cmake FindSomeLib cmake -- Installing   usr local lib SomeLib cmake HelperFile cmake   Now CMake has a find package   which opens a Find  cmake file and searches after the library on the system and defines some variables like SomeLib FOUND etc   My CMakeLists txt contains something like this   set CMAKE MODULE PATH   usr local lib SomeLib cmake    CMAKE MODULE PATH    find package SomeLib REQUIRED    The first command defines where CMake searches after the Find  cmake and I added the directory of SomeLib where the FindSomeLib cmake can be found  so find package   works  as expected   But this is kind of weird because one of the reasons why find package   exists is to get away from non-cross-plattform hard coded paths   How is this usually done  Should I copy the cmake  directory of SomeLib into my project and set the CMAKE MODULE PATH relatively

User · Accepted Answer

Command find package has two modes  Module mode and Config mode  You are trying to use Module mode when you actually need Config mode   Module mode  Find lt package gt  cmake file located within your project  Something like this   CMakeLists txt cmake FindFoo cmake cmake FindBoo cmake   CMakeLists txt content   list APPEND CMAKE MODULE PATH    CMAKE CURRENT LIST DIR  cmake   find package Foo REQUIRED    FOO INCLUDE DIR  FOO LIBRARIES find package Boo REQUIRED    BOO INCLUDE DIR  BOO LIBRARIES  include directories    FOO INCLUDE DIR    include directories    BOO INCLUDE DIR    add executable Bar Bar hpp Bar cpp  target link libraries Bar   FOO LIBRARIES    BOO LIBRARIES     Note that CMAKE MODULE PATH has high priority and may be usefull when you need to rewrite standard Find lt package gt  cmake file   Config mode  install    lt package gt Config cmake file located outside and produced by install command of other project  Foo for example    foo library    gt  cat CMakeLists txt  cmake minimum required VERSION 2 8  project Foo   add library foo Foo hpp Foo cpp  install FILES Foo hpp DESTINATION include  install TARGETS foo DESTINATION lib  install FILES FooConfig cmake DESTINATION lib cmake Foo    Simplified version of config file    gt  cat FooConfig cmake  add library foo STATIC IMPORTED  find library FOO LIBRARY PATH foo HINTS    CMAKE CURRENT LIST DIR           set target properties foo PROPERTIES IMPORTED LOCATION    FOO LIBRARY PATH      By default project installed in CMAKE INSTALL PREFIX directory    gt  cmake -H  -B builds  gt  cmake --build  builds --target install -- Install configuration     -- Installing   usr local include Foo hpp -- Installing   usr local lib libfoo a -- Installing   usr local lib cmake Foo FooConfig cmake   Config mode  use   Use find package     CONFIG  to include FooConfig cmake with imported target foo    gt  cat CMakeLists txt  cmake minimum required VERSION 2 8  project Boo     import library target  foo  find package Foo CONFIG REQUIRED   add executable boo Boo cpp Boo hpp  target link libraries boo foo   gt  cmake -H  -B builds -DCMAKE VERBOSE MAKEFILE ON  gt  cmake --build  builds Linking CXX executable Boo  usr bin c       -o Boo  usr local lib libfoo a   Note that imported target is highly configurable  See my answer   Update   Example

User · Answer

If you are running cmake to generate SomeLib yourself  say as part of a superbuild   consider using the User Package Registry  This requires no hard-coded paths and is cross-platform  On Windows  including mingw64  it works via the registry  If you examine how the list of installation prefixes is constructed by the CONFIG mode of the find packages   command  you ll see that the User Package Registry is one of elements   Brief how-to  Associate the targets of SomeLib that you need outside of that external project  by adding them to an export set in the CMakeLists txt files where they are created   add library thingInSomeLib      install TARGETS thingInSomeLib Export SomeLib-export DESTINATION lib    Create a XXXConfig cmake file for SomeLib in its   CMAKE CURRENT BUILD DIR  and store this location in the User Package Registry by adding two calls to export   to the CMakeLists txt associated with SomeLib   export EXPORT SomeLib-export NAMESPACE SomeLib   FILE SomeLibConfig cmake    Create SomeLibConfig cmake export PACKAGE SomeLib                                                       Store location of SomeLibConfig cmake   Issue your find package SomeLib REQUIRED  commmand in the CMakeLists txt file of the project that depends on SomeLib without the  non-cross-platform hard coded paths  tinkering with the CMAKE MODULE PATH   When it might be the right approach  This approach is probably best suited for situations where you ll never use your software downstream of the build directory  e g   you re cross-compiling and never install anything on your machine  or you re building the software just to run tests in the build directory   since it creates a link to a  cmake file in your  build  output  which may be temporary   But if you re never actually installing SomeLib in your workflow  calling EXPORT PACKAGE  lt name gt   allows you to avoid the hard-coded path  And  of course  if you are installing SomeLib  you probably know your platform  CMAKE MODULE PATH  etc  so  user2288008 s excellent answer will have you covered

User · Answer

How is this usually done  Should I copy the cmake  directory of SomeLib into my project and set the CMAKE MODULE PATH relatively    If you don t trust CMake to have that module  then - yes  do that - sort of  Copy the find SomeLib cmake and its dependencies into your cmake  directory  That s what I do as a fallback  It s an ugly solution though   Note that the FindFoo cmake modules are each a sort of a bridge between platform-dependence and platform-independence - they look in various platform-specific places to obtain paths in variables whose names is platform-independent

User · Answer

You don t need to specify the module path per se  CMake ships with its own set of built-in find package scripts  and their location is in the default CMAKE MODULE PATH   The more normal use case for dependent projects that have been CMakeified would be to use CMake s external project command and then include the Use Project  cmake file from the subproject  If you just need the Find Project  cmake script  copy it out of the subproject and into your own project s source code  and then you won t need to augment the CMAKE MODULE PATH in order to find the subproject at the system level

[cmake] What use is find_package() if you need to specify CMAKE_MODULE_PATH anyway?

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