[CMake] Using ExternalProject_Add

[Eric Noulard]

2011/12/29 Ryan Lewis <me at ryanlewis.net>:
[...]
>
> Also I cannot get the ExternalProject_Add() module to work properly.
>
>    include(ExternalProject)
>    ExternalProject_Add( JPEG
>    PREFIX ${CURRENT_SOURCE_DIR}

CURRENT_SOURCE_DIR is probably a typo:

you certainly mean:

CMAKE_CURRENT_SOURCE_DIR

[...]

> This command is also creating a folder structure called JPEG-prefix
> which does not seem to contain relevant/useful content..
>
> What am I doing wrong?

The typo, ${CURRENT_SOURCE_DIR} evaluate to empty string "".

try that:

include(ExternalProject)

ExternalProject_Add(MyZLib
                    PREFIX "/tmp/TestZlib/1.2.5"
                    URL "http://zlib.net/zlib-1.2.5.tar.bz2"
		    URL_MD5 "be1e89810e66150f5b0327984d8625a0"
                    PATCH_COMMAND ${CMAKE_COMMAND} -E remove -f
<SOURCE_DIR>/zconf.h
                    CMAKE_ARGS
"-DCMAKE_INSTALL_PREFIX=/tmp/TestZlib/1.2.5/installed"
                    )

it should download and locally install zlib during the first build.
Note that you cannot use ExternalProject_Add in order to download & build
a local dependency of the currently built project because it will be invoked
**at build time** so that at CMake **first-time** (when you configure
your project for the first time)
the external project is not build yet.

I suggest you read at least some mailing threads about ExternalProject_Add usage
they should be enlightening:
http://www.cmake.org/pipermail/cmake/2011-September/046423.html
http://www.cmake.org/pipermail/cmake/2011-September/046233.html
http://www.cmake.org/pipermail/cmake/2011-September/046360.html


-- 
Erk
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