[CMake] Don't download external projects again after calling "make clean"

[Cedric Doucet]

Hello David,

thank you very much for your help.

Unfortunately I may do something wrong because it does not work.
After cleaning, the library is downloaded again.

I guess my mistake comes from the fact I do not understand the role of URL_MD5.
Below is a simple example where downloading and installing is very fast.
You just have to replace the value of EXTERNAL_DIR by the path to your own "Downloads" repository.
I tried to put URL in my DOWNLOAD_COMMAND but the call "wget <URL>" does not seem to be understood by the wget command.

Thanks again!

Cédric

--------------------------------------------------------------------------
cmake_minimum_required (VERSION 2.6)

project (example CXX)

set(CMAKE_VERBOSE_MAKEFILE ON)

include(ProcessorCount)
ProcessorCount(N)
if(NOT N EQUAL 0)
  set(CMAKE_BUILD_FLAGS -j${N})
endif()

include(ExternalProject)
set(EXTERNAL_DIR /home/cdoucet/Downloads)
ExternalProject_Add(eigen
                    PREFIX ${EXTERNAL_DIR}/eigen
                    DOWNLOAD_DIR ${EXTERNAL_DIR}/eigen/download
                    SOURCE_DIR ${EXTERNAL_DIR}/eigen/src
                    BINARY_DIR ${EXTERNAL_DIR}/eigen/build
                    INSTALL_DIR ${EXTERNAL_DIR}/eigen/install
                    URL http://bitbucket.org/eigen/eigen/get/3.2.4.tar.gz
                    URL_MD5 ccb18a771f678b38a3d33c321a8e7daf
                    DOWNLOAD_COMMAND wget http://bitbucket.org/eigen/eigen/get/3.2.4.tar.gz && tar xvzf 3.2.4.tar.gz -C <SOURCE_DIR> --strip-components=1
                    CONFIGURE_COMMAND cd <BINARY_DIR> && cmake -D CMAKE_INSTALL_PREFIX=$<INSTALL_DIR> <SOURCE_DIR>
                   )
------------------------------------------------------------------------------



----- Mail original -----
> De: "David Cole" <DLRdave at aol.com>
> À: "Cedric Doucet" <cedric.doucet at inria.fr>
> Cc: cmake at cmake.org
> Envoyé: Lundi 13 Avril 2015 12:40:34
> Objet: Re: [CMake] Don't download external projects again after calling "make clean"
> 
> Use the URL_MD5 and DOWNLOAD_DIR arguments to ExternalProject_Add to
> put the downloaded files into a location outside the build tree
> (perhaps ~/Downloads on Mac/Linux or $ENV{USERPROFILE}/Downloads on
> Windows).
> 
> With DOWNLOAD_DIR outside the build tree, and the checksums of the
> downloaded files being the same as you've specified via URL_MD5, the
> download portion will be avoided once there is a local copy of a file
> available.
> 
> 
> HTH,
> David C.
> 
> 
> On Mon, Apr 13, 2015 at 5:04 AM, Cedric Doucet <cedric.doucet at inria.fr>
> wrote:
> >
> > Hello!
> >
> > I use the ExternalProject_Add function to download third-party libraries of
> > a code.
> >
> > Once a library has been downloaded, I can call "make" as many times as I
> > want without downloading this library again.
> > It seems that CMake detects that the library has already been downloaded.
> >
> > However, calling "make clean" seems to destroy this feature.
> > Even if my library is not uninstalled during cleaning, calling "make" after
> > "make clean" will lead CMake to try download the library again.
> >
> > How could I tell CMake not to download the library again?
> >
> > Thank you very much for your help!
> >
> > Cédric
> >
> > --
> >
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