[CMake] call already made makefile

[Alan W. Irwin]

On 2010-11-04 16:29-0700 SK wrote:

> On Sat, Oct 30, 2010 at 8:31 AM, Alan W. Irwin
> <irwin at beluga.phys.uvic.ca> wrote:
>> On 2010-10-29 20:50-0700 mina adel wrote:
>>
>>>
>>> Hi All
>>>
>>> I have an open source code that I use in my project. This open source code
>>> already has Makefile coded for it.
>>>
>>> I want to use cmake so that before it compile my project it first call the
>>> cmake of these open source code, which will compile it to .la library.
>>
>> ..make?
>>>
>>> Then using this library, it compile my code.
>>
>> I assume from the context you mean make rather than cmake above.
>>
>> To run make (or any command) at run-time, use the combination of
>> add_custom_command and add_custom_target.  Basically,
>> add_custom_command creates an OUTPUT file (say your library) at run
>> time, and add_custom_target file-depends on that file and creates a
>> CMake target corresponding to the custom command which you can add as
>> a dependency of your application target.  This insures make will be run (if
>> the library is not up to date) before your application is built.
>>
>
> No, this does not work when the external command is a make process.
> The problem is that the "output" of add_custom_command() is a target
> with it's own dependencies.

I don't understand your remark since the OUTPUT of add_custom_command
must refer to a file not a target, and there is a big distinction
between those two concepts in CMake.  That's why I emphasize when
a file is indicated and when a target is indicated below.

> The external make process must always run
> in order catch dependencies that only the external make knows about.
> The only way to make sure the make process always runs is to use
> add_custom_target(), but alas, add_custom_target does allow us to
> specify an output.
>
> See this thread from a few days ago: add_custom_command depends on
> output from add_custom_target.
>
> As far as I know, there is no satisfactory way to do use external
> makefiles with CMake.  I'm all ears if anyone has suggestions.
>

In the past I have been able to use an external set of Makefiles with
no problems. However, I eventually took my own advice and replaced
that method with one that used cmake.  So I don't have any current
good examples, and my remarks below are from memory. However, I think
it should be completely straightforward to do what you like if you
read the cmake documentation for add_custom_command and
add_custom_target carefully.

Here is schematically what you have to do:

add_custom_command(
   OUTPUT full_path_to_generated_library
   COMMAND make
   WORKING_DIRECTORY full_path to where Makefile is located
   )

add_custom_target(
   extern_lib
   DEPENDS full_path_to_generated_library
   )

add_executable(myexecutable myexcutable.c)

target_link_libraries(myexecutable full_path_to_generated_library)

add_dependencies(myexecutable extern_lib)

In sum, target_link_libraries tells how to link the executable file
associated with the myexecutable target to the library _file_
full_path_to_generated_library, add_dependencies makes sure the
_custom target_ extern_lib is built before the _target_ myexecutable is
built, and the _file_ DEPENDS of add_custom_target makes sure the
custom make command is run every time there is an attempt to build the
myexecutable (and therefore extern_lib) target.

Please check my memory of the correct way to do this by using the
touch command.  For example, if you touch one of the source files for
the external library, then I believe with the above scenario if you
subsequently run "make myexecutable", then the custom make command
should always be run (since it has no DEPENDS option), and therefore
the external library will automatically be rebuilt (assuming those
external Makefiles had done their dependencies properly), and
myexecutable relinked.

Of course, use "make VERBOSE=1" to follow exactly what commands are
being run when testing file dependencies and associated target
dependencies with the touch command.  Also, I believe it ultimately
would be a good idea to replace all builds of external libraries with
CMake-based builds since that gives you the most control of your
library organization.

Alan
__________________________
Alan W. Irwin

Astronomical research affiliation with Department of Physics and Astronomy,
University of Victoria (astrowww.phys.uvic.ca).

Programming affiliations with the FreeEOS equation-of-state implementation
for stellar interiors (freeeos.sf.net); PLplot scientific plotting software
package (plplot.org); the libLASi project (unifont.org/lasi); the Loads of
Linux Links project (loll.sf.net); and the Linux Brochure Project
(lbproject.sf.net).
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