Edit: my question targets the early configure stage where CMake input files are still being parsed and thus have to be present before include() is being called. So the answer found here: Force CMake to generate configure_file target every build does not solve my problem since it generates files after include() statements have been interpreted.
I have a CMakeLists.txt that includes a file which is generated in the configure stage:
execute_process(COMMAND "my-generator -o generated.cmake")
include(generated.cmake)
Apart from the fact that this approach doesn't feel right (not to say elegant) I now need to re-generate that file before every build (my-generator produces output that incorporates the current time).
My assumption is that I can't use add_custom_command() or add_custom_target() because the file would be generated at compile time but needed in the configure-step.
This very old post suggests to touch the input file so I did this:
execute_process(
COMMAND "my-generator -o generated.cmake"
COMMAND cmake -E touch "${CMAKE_CURRENT_LIST_FILE}")
.. which does not produce errors but calling make multiple times won't run the configure step more than once.
What do I do wrong? Is there a better approach?
Related
I'm trying to use add_custom_command to generate a file during the build. The command never seemed to be run, so I made this test file.
cmake_minimum_required( VERSION 2.6 )
add_custom_command(
OUTPUT hello.txt
COMMAND touch hello.txt
DEPENDS hello.txt
)
I tried running:
cmake .
make
And hello.txt was not generated. What have I done wrong?
The add_custom_target(run ALL ... solution will work for simple cases when you only have one target you're building, but breaks down when you have multiple top level targets, e.g. app and tests.
I ran into this same problem when I was trying to package up some test data files into an object file so my unit tests wouldn't depend on anything external. I solved it using add_custom_command and some additional dependency magic with set_property.
add_custom_command(
OUTPUT testData.cpp
COMMAND reswrap
ARGS testData.src > testData.cpp
DEPENDS testData.src
)
set_property(SOURCE unit-tests.cpp APPEND PROPERTY OBJECT_DEPENDS testData.cpp)
add_executable(app main.cpp)
add_executable(tests unit-tests.cpp)
So now testData.cpp will generated before unit-tests.cpp is compiled, and any time testData.src changes. If the command you're calling is really slow you get the added bonus that when you build just the app target you won't have to wait around for that command (which only the tests executable needs) to finish.
It's not shown above, but careful application of ${PROJECT_BINARY_DIR}, ${PROJECT_SOURCE_DIR} and include_directories() will keep your source tree clean of generated files.
Add the following:
add_custom_target(run ALL
DEPENDS hello.txt)
If you're familiar with makefiles, this means:
all: run
run: hello.txt
The problem with two existing answers is that they either make the dependency global (add_custom_target(name ALL ...)), or they assign it to a specific, single file (set_property(...)) which gets obnoxious if you have many files that need it as a dependency. Instead what we want is a target that we can make a dependency of another target.
The way to do this is to use add_custom_command to define the rule, and then add_custom_target to define a new target based on that rule. Then you can add that target as a dependency of another target via add_dependencies.
# this defines the build rule for some_file
add_custom_command(
OUTPUT some_file
COMMAND ...
)
# create a target that includes some_file, this gives us a name that we can use later
add_custom_target(
some_target
DEPENDS some_file
)
# then let's suppose we're creating a library
add_library(some_library some_other_file.c)
# we can add the target as a dependency, and it will affect only this library
add_dependencies(some_library some_target)
The advantages of this approach:
some_target is not a dependency for ALL, which means you only build it when it's required by a specific target. (Whereas add_custom_target(name ALL ...) would build it unconditionally for all targets.)
Because some_target is a dependency for the library as a whole, it will get built before all of the files in that library. That means that if there are many files in the library, we don't have to do set_property on every single one of them.
If we add DEPENDS to add_custom_command then it will only get rebuilt when its inputs change. (Compare this to the approach that uses add_custom_target(name ALL ...) where the command gets run on every build regardless of whether it needs to or not.)
For more information on why things work this way, see this blog post: https://samthursfield.wordpress.com/2015/11/21/cmake-dependencies-between-targets-and-files-and-custom-commands/
This question is pretty old, but even if I follow the suggested recommendations, it does not work for me (at least not every time).
I am using Android Studio and I need to call cMake to build C++ library. It works fine until I add the code to run my custom script (in fact, at the moment I try to run 'touch', as in the example above).
First of,
add_custom_command
does not work at all.
I tried
execute_process (
COMMAND touch hello.txt
)
it works, but not every time!
I tried to clean the project, remove the created file(s) manually, same thing.
Tried cMake versions:
3.10.2
3.18.1
3.22.1
when they work, they produce different results, depending on cMake version, one file or several. This is not that important as long as they work, but that's the issue.
Can somebody shed light on this mystery?
I'm trying to use add_custom_command to generate a file during the build. The command never seemed to be run, so I made this test file.
cmake_minimum_required( VERSION 2.6 )
add_custom_command(
OUTPUT hello.txt
COMMAND touch hello.txt
DEPENDS hello.txt
)
I tried running:
cmake .
make
And hello.txt was not generated. What have I done wrong?
The add_custom_target(run ALL ... solution will work for simple cases when you only have one target you're building, but breaks down when you have multiple top level targets, e.g. app and tests.
I ran into this same problem when I was trying to package up some test data files into an object file so my unit tests wouldn't depend on anything external. I solved it using add_custom_command and some additional dependency magic with set_property.
add_custom_command(
OUTPUT testData.cpp
COMMAND reswrap
ARGS testData.src > testData.cpp
DEPENDS testData.src
)
set_property(SOURCE unit-tests.cpp APPEND PROPERTY OBJECT_DEPENDS testData.cpp)
add_executable(app main.cpp)
add_executable(tests unit-tests.cpp)
So now testData.cpp will generated before unit-tests.cpp is compiled, and any time testData.src changes. If the command you're calling is really slow you get the added bonus that when you build just the app target you won't have to wait around for that command (which only the tests executable needs) to finish.
It's not shown above, but careful application of ${PROJECT_BINARY_DIR}, ${PROJECT_SOURCE_DIR} and include_directories() will keep your source tree clean of generated files.
Add the following:
add_custom_target(run ALL
DEPENDS hello.txt)
If you're familiar with makefiles, this means:
all: run
run: hello.txt
The problem with two existing answers is that they either make the dependency global (add_custom_target(name ALL ...)), or they assign it to a specific, single file (set_property(...)) which gets obnoxious if you have many files that need it as a dependency. Instead what we want is a target that we can make a dependency of another target.
The way to do this is to use add_custom_command to define the rule, and then add_custom_target to define a new target based on that rule. Then you can add that target as a dependency of another target via add_dependencies.
# this defines the build rule for some_file
add_custom_command(
OUTPUT some_file
COMMAND ...
)
# create a target that includes some_file, this gives us a name that we can use later
add_custom_target(
some_target
DEPENDS some_file
)
# then let's suppose we're creating a library
add_library(some_library some_other_file.c)
# we can add the target as a dependency, and it will affect only this library
add_dependencies(some_library some_target)
The advantages of this approach:
some_target is not a dependency for ALL, which means you only build it when it's required by a specific target. (Whereas add_custom_target(name ALL ...) would build it unconditionally for all targets.)
Because some_target is a dependency for the library as a whole, it will get built before all of the files in that library. That means that if there are many files in the library, we don't have to do set_property on every single one of them.
If we add DEPENDS to add_custom_command then it will only get rebuilt when its inputs change. (Compare this to the approach that uses add_custom_target(name ALL ...) where the command gets run on every build regardless of whether it needs to or not.)
For more information on why things work this way, see this blog post: https://samthursfield.wordpress.com/2015/11/21/cmake-dependencies-between-targets-and-files-and-custom-commands/
This question is pretty old, but even if I follow the suggested recommendations, it does not work for me (at least not every time).
I am using Android Studio and I need to call cMake to build C++ library. It works fine until I add the code to run my custom script (in fact, at the moment I try to run 'touch', as in the example above).
First of,
add_custom_command
does not work at all.
I tried
execute_process (
COMMAND touch hello.txt
)
it works, but not every time!
I tried to clean the project, remove the created file(s) manually, same thing.
Tried cMake versions:
3.10.2
3.18.1
3.22.1
when they work, they produce different results, depending on cMake version, one file or several. This is not that important as long as they work, but that's the issue.
Can somebody shed light on this mystery?
This is what typically happens. I get source code that has cmake build scripts. I create a build subdirectory, change to it, run cmake <options> ... Depending upon the project and its dependencies I have to repeat the last step until it finds all necessary dependencies and generates makefiles. I successfully build and use the project. Few days pass, I forget about this installation. Then one day I'm trying to setup the same project on another machine and now I can't recall what exact CMake command line I used in the past to get things working.
I still have the old build directory on the old machine. Can I find the cmake command line I used in the past, by looking into some of the autogenerated files in the build directory? I was expecting CMake would just put the exact command line I used in one of these files in commented form. But if it does so, I haven't found it yet.
How can I find the original CMake command line I used?
You can't.
Original CMake command can be guessed from analysis of CMakeCache.txt
As a workaround, you could always create a simple wrapper to store the original command line used. Something along these lines:
#!/bin/bash
echo "$#" > cmake_command.log
$#
I am trying to write a CMakeLists.txt to speed up compilation.
The executable depends on a script generated .cpp file: I use the cppcms web application library which has a templating system where .tmpl must be converted to .cpp files during the compilation like this:
cppcms_tmpl_cc page.tmpl -o page.cpp
There are related questions that cover the use of bash commands within cmake:
How to run a command at compile time within Makefile generated by CMake?
CMake : how to use bash command in CMakeLists.txt
These questions cover most of my needs.
What I want to know, now, is how to tell cmake to run the above command and re-generate page.cpp every time page.tmpl itself has changed, and only then?
The goal obviously is to improve the compile time and have an up to date binary with the latest template.
(can a moderator add the cppcms tag?)
[Edit: I am actually trying to convert the following Makefile to cmake:
LIBS=-lcppcms -lconfig++ -lboost_filesystem-mt
all: clean gitbrowser
gitbrowser: main.cpp view.cpp content.hpp gitbrowser.cpp
$(CXX) -Wall main.cpp gitbrowser.cpp view.cpp -o run ${LIBS}
view.cpp: page.tmpl content.hpp
cppcms_tmpl_cc page.tmpl -o view.cpp
[Edit2: I added a note about the solution in the official cppcms wiki:
http://art-blog.no-ip.info/wikipp/en/page/cppcms_1x_howto#How.to.compile.the.templates.with.cmake.
now = get_now_time()
time = get_last_upd_time()
if (now > time)
set (LAST_UPD_TIME time CACHE INTERNAL "Defines last update time of the file" FORCE)
# run bash command here
endif (now > time)
get_now_time and get_last_upd_time are fictional functions, returning timestamps (I guess you can use bash commands to get those timestamps). Then you can compare them and store last modification timestamp into cache.
However, this solution looks ugly for me, as I know if you properly define targets and dependencies between them CMake itself will take care of rebuilding only modified files, doesn't it? Could you show me target definitions?
edit
You can use following CMakeLists.txt (thougn I'm not sure, it's based on my project):
# add main target, the executable file
ADD_EXECUTABLE(gitbrowser main.cpp view.cpp content.hpp gitbrowser.cpp)
# linking it with necessary libraries
TARGET_LINK_LIBRARIES(gitbrowser "cppcms config++ boost_filesystem-mt")
# add page.cpp target
ADD_CUSTOM_COMMAND(
OUTPUT page.cpp
COMMAND "cppcms_tmpl_cc page.tmpl -o view.cpp"
DEPENDS page.tmpl content.hpp
)
# and finally add dependency of the main target
ADD_DEPENDENCIES(gitbrowser page.cpp)
Good luck
Take a look on this CMake file of Wikipp lines 66-72
You basically need something like this:
add_custom_command(
OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/view.cpp
COMMAND cppcms_tmpl_cc
view.tmpl
-o ${CMAKE_CURRENT_BINARY_DIR}/view.cpp
DEPENDS view.tmpl)
Edit: Also if you want to improve compilation speed you may compile
the view into shared object and load it dynamically.
This would also allow you not to restart application if you only changed the view, the
shared object after recompilation would be automatically reloaded.
See: http://art-blog.no-ip.info/wikipp/en/page/cppcms_1x_config#views for more details.
I'm trying to use add_custom_command to generate a file during the build. The command never seemed to be run, so I made this test file.
cmake_minimum_required( VERSION 2.6 )
add_custom_command(
OUTPUT hello.txt
COMMAND touch hello.txt
DEPENDS hello.txt
)
I tried running:
cmake .
make
And hello.txt was not generated. What have I done wrong?
The add_custom_target(run ALL ... solution will work for simple cases when you only have one target you're building, but breaks down when you have multiple top level targets, e.g. app and tests.
I ran into this same problem when I was trying to package up some test data files into an object file so my unit tests wouldn't depend on anything external. I solved it using add_custom_command and some additional dependency magic with set_property.
add_custom_command(
OUTPUT testData.cpp
COMMAND reswrap
ARGS testData.src > testData.cpp
DEPENDS testData.src
)
set_property(SOURCE unit-tests.cpp APPEND PROPERTY OBJECT_DEPENDS testData.cpp)
add_executable(app main.cpp)
add_executable(tests unit-tests.cpp)
So now testData.cpp will generated before unit-tests.cpp is compiled, and any time testData.src changes. If the command you're calling is really slow you get the added bonus that when you build just the app target you won't have to wait around for that command (which only the tests executable needs) to finish.
It's not shown above, but careful application of ${PROJECT_BINARY_DIR}, ${PROJECT_SOURCE_DIR} and include_directories() will keep your source tree clean of generated files.
Add the following:
add_custom_target(run ALL
DEPENDS hello.txt)
If you're familiar with makefiles, this means:
all: run
run: hello.txt
The problem with two existing answers is that they either make the dependency global (add_custom_target(name ALL ...)), or they assign it to a specific, single file (set_property(...)) which gets obnoxious if you have many files that need it as a dependency. Instead what we want is a target that we can make a dependency of another target.
The way to do this is to use add_custom_command to define the rule, and then add_custom_target to define a new target based on that rule. Then you can add that target as a dependency of another target via add_dependencies.
# this defines the build rule for some_file
add_custom_command(
OUTPUT some_file
COMMAND ...
)
# create a target that includes some_file, this gives us a name that we can use later
add_custom_target(
some_target
DEPENDS some_file
)
# then let's suppose we're creating a library
add_library(some_library some_other_file.c)
# we can add the target as a dependency, and it will affect only this library
add_dependencies(some_library some_target)
The advantages of this approach:
some_target is not a dependency for ALL, which means you only build it when it's required by a specific target. (Whereas add_custom_target(name ALL ...) would build it unconditionally for all targets.)
Because some_target is a dependency for the library as a whole, it will get built before all of the files in that library. That means that if there are many files in the library, we don't have to do set_property on every single one of them.
If we add DEPENDS to add_custom_command then it will only get rebuilt when its inputs change. (Compare this to the approach that uses add_custom_target(name ALL ...) where the command gets run on every build regardless of whether it needs to or not.)
For more information on why things work this way, see this blog post: https://samthursfield.wordpress.com/2015/11/21/cmake-dependencies-between-targets-and-files-and-custom-commands/
This question is pretty old, but even if I follow the suggested recommendations, it does not work for me (at least not every time).
I am using Android Studio and I need to call cMake to build C++ library. It works fine until I add the code to run my custom script (in fact, at the moment I try to run 'touch', as in the example above).
First of,
add_custom_command
does not work at all.
I tried
execute_process (
COMMAND touch hello.txt
)
it works, but not every time!
I tried to clean the project, remove the created file(s) manually, same thing.
Tried cMake versions:
3.10.2
3.18.1
3.22.1
when they work, they produce different results, depending on cMake version, one file or several. This is not that important as long as they work, but that's the issue.
Can somebody shed light on this mystery?