[CMake] Generated files?

Fri Jan 30 10:11:04 EST 2015

As you say, **make** is fairly powerful at this. Other build tools may not
be, it might even be an alien concept to them. AFAIK, Ninja requires an
explicit list of files & dependencies, for example. Visual Studio solutions
can only contain explicitly listed files too.

CMake projects are supposed to work with all generators which CMake
supports (within reason). There are some generator-specific features in
CMake, but the intent is to keep the set of these to a minimum.

The list of CMake commands which directly create build-time "commands"
(such as Makefile rules) is rather short:

add_custom_command()
add_custom_target()
add_executable()
add_library()

Other commands modify the buildsystem (e.g. add_definitions(),
target_link_libraries(), or setting properties such as COMPILE_OPTIONS),
but they don't really add "commands" to it.

Petr

On Fri, Jan 30, 2015 at 3:27 PM, Chris Johnson <cxjohnson at gmail.com> wrote:

> That does clarify a few things yes.  Thank you.
>
> By "configure" time I had meant the first two items you listed as
> Configure and Generate.  By "run" time I had meant what you called Build.
>
> One place I am unclear on is exactly which commands in CMakeLists.txt get
> translated into Build time commands in buildsystem files (in my case,
> make).  For example, make is fairly powerful at generating substitution
> file names, e.g. creating prog.o from prog.cpp, or file1.out from file1.in.
> Make is also capable of running full shell scripts within a makefile.  But
> there's no obvious way to drive any kind of automation from CMake that make
> is capable of.
>
> As a programmer, my first thought when having to process a large list of
> files is to do it through some sort of automation, rather than generate a
> brute force solution.  It appears that with CMake, the best one can hope
> for is to automate the creation of the brute-force solution.
>
> --
> Cheers,
> ..chris
>
> On Fri, Jan 30, 2015 at 4:32 AM, Petr Kmoch <petr.kmoch at gmail.com> wrote:
>
>> It's not clear to me what you mean with "run" time. There are the
>> following "times" involved in a CMake-based project:
>>
>> * Configure time:
>> CMake is parsing CMakeLists.txt files and files included from those and
>> executing ALL CMake commands found in them. Variables expansion takes
>> place. Data structures in CMake's memory are filled.
>>
>> * Generate time:
>> CMake processes the data structures in its memory to write buildsystem
>> files (Makefiles, solutions etc.) to disk. Generator expressions are
>> expanded. Files are generated from data specified in file(GENERATE ...)
>> commands. cmake_install.cmake file is written based on the contents of data
>> structures filled by install() commands.
>>
>> * Build time:
>> CMake is not running (except for driving the build if you do that with
>> `cmake --build`). The build tool (make, ninja, devenv, msbuild, ...) is
>> running, processing the buildsystem files and generating compiled binaries.
>> At this time, commands which were set up by add_custom_command() and
>> add_custom_target() are executed as driven by the build tool.
>>
>> * Install time (optional):
>> Running `make install` or similarly triggering the install process causes
>> CMake to run in installation mode. This CMake reads the cmake_install.cmake
>> file and executes the commands there. These are mainly file() commands
>> which copy files to the desired location.
>>
>> CMake commands in CMakeLists.txt and included files are all executed
>> during configure time, as the files are parsed and processed by CMake. Some
>> of these commands have immediate effects on the outside environment (e.g.
>> file(WRITE), execute_process(), try_compile()), some affect the CMake
>> processing control flow (e.g. include(), foreach()), some fill in or modify
>> CMake's data structures (e.g. set(), add_executable(), install(),
>> add_custom_command()).
>>
>> So there are no CMake commands executed after configure time. The value
>> specified in a COMMAND argument of add_custom_command() executes at build
>> time (driven by the build system), but the add_custom_command() itself
>> executes at CMake time.
>>
>> I hope I've clarified it a little bit.
>>
>> Petr
>>
>>
>>
>> On Thu, Jan 29, 2015 at 9:36 PM, Chris Johnson <cxjohnson at gmail.com>
>> wrote:
>>
>>> Thanks; I appreciate the suggestions.
>>>
>>> One thing that jumped out is the thought that foreach() is executed at
>>> "configuration" time, not "run" time.  To me, that was counter-intuitive,
>>> but makes more sense once more thoroughly considered.
>>>
>>> But I have to admit, I've never seen anything in the documentation which
>>> lists all of the commands which execute at configuration time, and which
>>> are executed at run time.  Is there such documentation?  A link to it would
>>> be great.
>>>
>>> On Thu, Jan 29, 2015 at 9:51 AM, Thompson, KT <kgt at lanl.gov> wrote:
>>>
>>>>  Hi Chris,
>>>>
>>>>
>>>>
>>>> Why not use a foreach loop? Something like this…
>>>>
>>>>
>>>>
>>>> add_executable(myprog myprog.cpp)
>>>>
>>>> set( files file001 fiile002 …)
>>>>
>>>> foreach( file in files)
>>>>
>>>>     add_custom_command(OUTPUT ${file}.out
>>>>
>>>>         COMMAND /bin/cp ${CMAKE_CURRENT_SOURCE_DIR}/${file}.in .
>>>>
>>>>         COMMAND myprog ${file}.in ${file}.out
>>>>
>>>>         DEPENDS ${file}.in myprog.cpp
>>>>
>>>>     )
>>>>
>>>> endforeach()
>>>>
>>>>
>>>>
>>>> For portability, you might want to use ‘${CMAKE_COMMAND} –E
>>>> copy_if_different’ in place of ‘/bin/cp’ and CMAKE_CURRENT_BINARY_DIR in
>>>> place of ‘.’
>>>>
>>>>
>>>>
>>>> -kt
>>>>
>>>>
>>>>
>>>> *From:* CMake [mailto:cmake-bounces at cmake.org] *On Behalf Of *Chris
>>>> Johnson
>>>> *Sent:* Thursday, January 29, 2015 8:09 AM
>>>> *To:* cmake at cmake.org
>>>> *Subject:* [CMake] Generated files?
>>>>
>>>>
>>>>
>>>> I am looking for suggestions on how to solve the following problem.
>>>> I need a solution which is easy to understand and safe from future
>>>> maintenance errors.
>>>>
>>>>
>>>>
>>>> There is a project directory with one C++ program and a large number of
>>>> "input" data files.
>>>>
>>>>
>>>>
>>>> The C++ program needs to be compiled, and then run against each of the
>>>> input files to generate an output file of the same base name but with a
>>>> different output suffix.  E.g. from the command line it might be:
>>>>
>>>>
>>>>
>>>>     % myprog  file001.in  file001.out
>>>>
>>>>
>>>>
>>>> Finally, the output files need to be installed in the proper location.
>>>>
>>>>
>>>>
>>>> For one input file, it might look like this:
>>>>
>>>>
>>>>
>>>>     add_executable(myprog myprog.cpp)
>>>>
>>>>     add_custom_command(OUTPUT file001.out
>>>>
>>>>         COMMAND /bin/cp ${CMAKE_CURRENT_SOURCE_DIR}/file001.in .
>>>>
>>>>         COMMAND myprog file001.in file001.out
>>>>
>>>>         DEPENDS files001.in myprog.cpp
>>>>
>>>>     )
>>>>
>>>>     install(FILES ${CMAKE_CURRENT_BINARY_DIR}/file001.out DESTINATION
>>>> share/docs)
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> Listing all of the input files in my CMakeLists.txt file is not a
>>>> problem, but it would be nice to avoid having to list the corresponding
>>>> output files.
>>>>
>>>>
>>>>
>>>> How can I build a CMakeLists.txt file which will succinctly handle this
>>>> situation?
>>>>
>>>>
>>>>
>>>> --
>>>>
>>>> Thanks,
>>>>
>>>> ..chris
>>>>
>>>
>>>
>>> --
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>>
>>
>
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