CMake How to build external projects and include their targets

Question

I have a Project A that exports a static library as a target   install TARGETS alib DESTINATION lib EXPORT project a-targets  install EXPORT project a-targets DESTINATION lib alib    Now I want to use Project A as an external project from Project B and include its built targets   ExternalProject Add project a   URL    project a tar gz   PREFIX   CMAKE CURRENT BINARY DIR  project a   CMAKE ARGS -DCMAKE INSTALL PREFIX PATH  lt INSTALL DIR gt     include   CMAKE CURRENT BINARY DIR  lib project a project a-targets cmake    The problem is that the include file does not exist yet when CMakeLists of Project B is run   Is there a way to make the include dependent on the external project being built   Update  I wrote a short CMake by Example tutorial based on this and other common problems I encountered

User · Answer

I think you re mixing up two different paradigms here   As you noted  the highly flexible ExternalProject module runs its commands at build time  so you can t make direct use of Project A s import file since it s only created once Project A has been installed   If you want to include Project A s import file  you ll have to install Project A manually before invoking Project B s CMakeLists txt - just like any other third-party dependency added this way or via find file   find library   find package   If you want to make use of ExternalProject Add  you ll need to add something like the following to your CMakeLists txt   ExternalProject Add project a   URL    project a tar gz   PREFIX   CMAKE CURRENT BINARY DIR  project a   CMAKE ARGS -DCMAKE INSTALL PREFIX PATH  lt INSTALL DIR gt     include   CMAKE CURRENT BINARY DIR  lib project a project a-targets cmake   ExternalProject Get Property project a install dir  include directories   install dir  include   add dependencies project b exe project a  target link libraries project b exe   install dir  lib alib lib

User · Answer

I was searching for similar solution  The replies here and the Tutorial on top is informative  I studied posts blogs referred here to build mine successful  I am posting complete CMakeLists txt worked for me  I guess  this would be helpful as a basic template for beginners   quot CMakeLists txt quot  cmake minimum required VERSION 3 10 2     Target Project project  ClientProgram     Begin  Including Sources and Headers include directories include  file  GLOB SOURCES  quot src   c quot     End  Including Sources and Headers     Begin  Generate executables add executable  ClientProgram   SOURCES     End  Generate executables     This Project Depends on External Project s   include  ExternalProject     Begin  External Third Party Library set  libTLS ThirdPartyTlsLibrary  ExternalProject Add    libTLS  PREFIX            CMAKE CURRENT BINARY DIR    libTLS    Begin  Download Archive from Web Server URL             http   myproject com MyLibrary tgz URL HASH        SHA1  lt expected sha1sum of above tgz file gt  DOWNLOAD NO PROGRESS ON   End  Download Archive from Web Server    Begin  Download Source from GIT Repository      GIT REPOSITORY  https   github com  lt project gt  git      GIT TAG          lt Refer github com releases - gt  Tags gt       GIT SHALLOW     ON   End  Download Source from GIT Repository    Begin  CMAKE Comamnd Argiments CMAKE ARGS      -DCMAKE INSTALL PREFIX PATH   CMAKE CURRENT BINARY DIR    libTLS  CMAKE ARGS      -DUSE SHARED LIBRARY BOOL ON   End  CMAKE Comamnd Argiments          The above ExternalProject Add      construct wil take care of     1  Downloading sources   2  Building Object files   3  Install under DCMAKE INSTALL PREFIX Directory    Acquire Installation Directory of  ExternalProject Get Property    libTLS  install dir     Begin  Importing Headers  amp  Library of Third Party built using ExternalProject Add        Include PATH that has headers required by Target Project include directories    install dir  include     Import librarues from External Project required by Target Project add library  lmytls SHARED IMPORTED  set target properties  lmytls PROPERTIES IMPORTED LOCATION   install dir  lib libmytls so  add library  lmyxdot509 SHARED IMPORTED  set target properties lmyxdot509 PROPERTIES IMPORTED LOCATION   install dir  lib libmyxdot509 so     End  Importing Headers  amp  Library of Third Party built using ExternalProject Add        End  External Third Party Library    Begin  Target Project depends on Third Party Component add dependencies ClientProgram   libTLS     End  Target Project depends on Third Party Component    Refer libraries added above used by Target Project target link libraries  ClientProgram lmytls lmyxdot509

User · Answer

This post has a reasonable answer   CMakeLists txt in   cmake minimum required VERSION 2 8 2   project googletest-download NONE   include ExternalProject  ExternalProject Add googletest   GIT REPOSITORY    https   github com google googletest git   GIT TAG           master   SOURCE DIR           CMAKE BINARY DIR  googletest-src    BINARY DIR           CMAKE BINARY DIR  googletest-build    CONFIGURE COMMAND      BUILD COMMAND          INSTALL COMMAND        TEST COMMAND             CMakeLists txt     Download and unpack googletest at configure time configure file CMakeLists txt in                googletest-download CMakeLists txt  execute process COMMAND   CMAKE COMMAND  -G    CMAKE GENERATOR       WORKING DIRECTORY   CMAKE BINARY DIR  googletest-download   execute process COMMAND   CMAKE COMMAND  --build     WORKING DIRECTORY   CMAKE BINARY DIR  googletest-download      Prevent GoogleTest from overriding our compiler linker options   when building with Visual Studio set gtest force shared crt ON CACHE BOOL    FORCE     Add googletest directly to our build  This adds   the following targets  gtest  gtest main  gmock   and gmock main add subdirectory   CMAKE BINARY DIR  googletest-src                    CMAKE BINARY DIR  googletest-build     The gtest gmock targets carry header search path   dependencies automatically when using CMake 2 8 11 or   later  Otherwise we have to add them here ourselves  if  CMAKE VERSION VERSION LESS 2 8 11    include directories    gtest SOURCE DIR  include                           gmock SOURCE DIR  include   endif      Now simply link your own targets against gtest  gmock    etc  as appropriate   However it does seem quite hacky  I d like to propose an alternative solution - use Git submodules   cd MyProject dependencies gtest git submodule add https   github com google googletest git cd googletest git checkout release-1 8 0 cd          git add   git commit -m  Add googletest    Then in MyProject dependencies gtest CMakeList txt you can do something like   cmake minimum required VERSION 3 3   if TARGET gtest    To avoid diamond dependencies  may not be necessary depending on you project      return   endif    add subdirectory  googletest     I haven t tried this extensively yet but it seems cleaner   Edit  There is a downside to this approach  The subdirectory might run install   commands that you don t want  This post has an approach to disable them but it was buggy and didn t work for me   Edit 2  If you use add subdirectory  googletest  EXCLUDE FROM ALL  it seems means the install   commands in the subdirectory aren t used by default

User · Answer

Edit  CMake now has builtin support for this  See new answer   You can also force the build of the dependent target in a secondary make process  See my answer on a related topic

User · Answer

cmake s ExternalProject Add indeed can used  but what I did not like about it - is that it performs something during build  continuous poll  etc    I would prefer to build project during build phase  nothing else  I have tried to override ExternalProject Add in several attempts  unfortunately without success   Then I have tried also to add git submodule  but that drags whole git repository  while in certain cases I need only subset of whole git repository  What I have checked - it s indeed possible to perform sparse git checkout  but that require separate function  which I wrote below    -----------------------------------------------------------------------------     Performs sparse  partial  git checkout       into   checkoutDir  from   url  of   branch      List of folders and files to pull can be specified after that   ----------------------------------------------------------------------------- function  SparseGitCheckout checkoutDir url branch      if EXISTS   checkoutDir           return       endif        message  -------------------------------------------------------------------       message  sparse git checkout to   checkoutDir           message  -------------------------------------------------------------------        file MAKE DIRECTORY   checkoutDir        set cmds  git init       set cmds   cmds   git remote add -f origin --no-tags -t master   url        set cmds   cmds   git config core sparseCheckout true          This command is executed via file WRITE       echo  lt file or folder gt   gt  gt   git info sparse-checkout        set cmds   cmds   git pull --depth 1 origin   branch           message  In directory    checkoutDir         foreach  cmd   cmds           message  -   cmd            string REPLACE         cmdList   cmd             message  Outfile    outFile             message  Final command    cmdList             if pull IN LIST cmdList              string  REPLACE       n  FILES    ARGN                file WRITE   checkoutDir   git info sparse-checkout   FILES            endif            execute process              COMMAND   cmdList              WORKING DIRECTORY   checkoutDir              RESULT VARIABLE ret                    if NOT ret EQUAL  0               message  error  previous command failed  see explanation above               file REMOVE RECURSE   checkoutDir               break           endif       endforeach    endfunction     SparseGitCheckout   CMAKE BINARY DIR  catch 197 https   github com catchorg Catch2 git v1 9 7 single include  SparseGitCheckout   CMAKE BINARY DIR  catch master https   github com catchorg Catch2 git master single include    I have added two function calls below just to illustrate how to use the function   Someone might not like to checkout master   trunk  as that one might be broken - then it s always possible to specify specific tag   Checkout will be performed only once  until you clear the cache folder

[cmake] CMake: How to build external projects and include their targets

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