CMake: How to set dependency from executable to custom target

Question

I am using CMake on a linux environment using cmake 2.8.1. I also tried cmake 2.8.7 with the same results.

I need to do some special conditioning on an archive (static library). This is done as a cmake custom_command. The result is a new archive that should be used in the link of the executable. The input archive for the conditioning is also a cmake target.

What I need is a dependency between the conditioned version of the archive and the executable. Using add_dependencies doesn't work and I don't undestand why.

I created an example that shows that behaviour of cmake. The example contains 2 C Files, one for the archive and one containing main(). As simple archive conditioning I just make a copy of the previously generated archive.

Here are the 2 source files:

main.c:

int myPrint(void);

int main(void)
{
  myPrint();
}

mylib.c:

#include <stdio.h>

int myPrint(void)
{
  printf("Hello World\n");
}

This is the CMakeLists.txt I created:

cmake_minimum_required(VERSION 2.8)

project(cmake_dependency_test)

add_library(mylib STATIC mylib.c)

add_custom_command(OUTPUT libmylib_conditioned.a
                   COMMAND cp libmylib.a libmylib_conditioned.a
                   DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/libmylib.a
                   COMMENT "Conditioning library")
add_custom_target(conditioning DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/libmylib_conditioned.a)
add_dependencies(conditioning mylib)

add_executable(cmake_dependency_test main.c)
add_dependencies(cmake_dependency_test conditioning)
target_link_libraries(cmake_dependency_test -L. mylib_conditioned)

First I create the archive mylib. With add_custom_command I do the conditioning and add_custom_target provides a top level target for the conditioned archive. Since I need to update the input archive before the conditioned archive is built I added a dependency between the input archive top level target and the conditioned archive top level target. This works perfectly! When I touch mylib.c and run make conditioning the input archive is built and after that the conditioned archive.

Ok. Now I use the conditioned archive for linking. In order to have a dependency from the executable to the conditioned archive I used again add_dependencies. But touching the library source mylib.c and then running make will not update the executable as expected.

Where is the mistake in the CMakeLists.txt?

guini · Accepted Answer · 2013-01-21 12:47:18Z

2

You can try to set the target property LINK_DEPENDS for the target cmake_dependency_test.

...
add_executable(cmake_dependency_test main.c )  
set_property(TARGET cmake_dependency_test PROPERTY LINK_DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/libmylib_conditioned.a)  
add_dependencies(cmake_dependency_test conditioning mylib)
target_link_libraries(cmake_dependency_test -L. mylib_conditioned)

edited Jan 21, 2013 at 12:47

answered Jan 21, 2013 at 10:01

guini

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2 Comments

user1995197 Over a year ago

This could be an alternative for the depend. What is not working for me is the dependency of the executeable from the custom_command.

guini Over a year ago

I edited the answer. I tested it on Windows, but I hope it works for you to.

einpoklum · Accepted Answer · 2022-04-14 09:12:14Z

tl;dr: No mistake, it now works.

There is no mistake in your CMakeLists.txt, just a bug or missing bit of implementation in CMake.

With more recent versions of CMake, it will work. I recommend setting the minimum required version as high as you can (since it's very easy to get a recent version of CMake - the distributed binaries run almost anywhere since they have almost no shared-lib dependencies.) - to get newer behavior, avoid deprecation warnings etc.

If I set:

cmake_minimum_required(VERSION 3.3)

and configure, I get:

-- The C compiler identification is GNU 10.2.1
-- The CXX compiler identification is GNU 10.2.1
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: /tmp/delme/build

and when I build (with GNU Make in my case), I get:

[ 20%] Building C object CMakeFiles/mylib.dir/mylib.c.o
[ 40%] Linking C static library libmylib.a
[ 40%] Built target mylib
[ 60%] Conditioning library
[ 60%] Built target conditioning
[ 80%] Building C object CMakeFiles/cmake_dependency_test.dir/main.c.o
[100%] Linking C executable cmake_dependency_test
[100%] Built target cmake_dependency_test

So, problem solved, and it only took 9 years :-)

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