Looking around on the net I have seen a lot of code like this:
include(FindPkgConfig)
pkg_search_module(SDL2 REQUIRED sdl2)
target_include_directories(app SYSTEM PUBLIC ${SDL2_INCLUDE_DIRS})
target_link_libraries(app ${SDL2_LIBRARIES})
However that seems to be the wrong way about doing it, as it only uses the include directories and libraries, but ignored defines, library paths and other flags that might be returned by pkg-config.
What would be the correct way to do this and ensure that all compile and link flags returned by pkg-config are used by the compiled app? And is there a single command to accomplish this, i.e. something like target_use(app SDL2)?
ref:
include()
FindPkgConfig
First of, the call:
include(FindPkgConfig)
should be replaced with:
find_package(PkgConfig)
The find_package() call is more flexible and allows options such as REQUIRED, that do things automatically that one would have to do manually with include().
Secondly, manually calling pkg-config should be avoid when possible. CMake comes with a rich set of package definitions, found in Linux under /usr/share/cmake-3.0/Modules/Find*cmake. These provide more options and choice for the user than a raw call to pkg_search_module().
As for the mentioned hypothetical target_use() command, CMake already has that built-in in a way with PUBLIC|PRIVATE|INTERFACE. A call like target_include_directories(mytarget PUBLIC ...) will cause the include directories to be automatically used in every target that uses mytarget, e.g. target_link_libraries(myapp mytarget). However this mechanism seems to be only for libraries created within the CMakeLists.txt file and does not work for libraries acquired with pkg_search_module(). The call add_library(bar SHARED IMPORTED) might be used for that, but I haven't yet looked into that.
As for the main question, this here works in most cases:
find_package(PkgConfig REQUIRED)
pkg_check_modules(SDL2 REQUIRED sdl2)
...
target_link_libraries(testapp ${SDL2_LIBRARIES})
target_include_directories(testapp PUBLIC ${SDL2_INCLUDE_DIRS})
target_compile_options(testapp PUBLIC ${SDL2_CFLAGS_OTHER})
The SDL2_CFLAGS_OTHER contains defines and other flags necessary for a successful compile. The flags SDL2_LIBRARY_DIRS and SDL2_LDFLAGS_OTHER are however still ignored, no idea how often that would become a problem.
More documentation here http://www.cmake.org/cmake/help/latest/module/FindPkgConfig.html
If you're using cmake and pkg-config in a pretty normal way, this solution works.
If, however, you have a library that exists in some development directory (such as /home/me/hack/lib), then using other methods seen here fail to configure the linker paths. Libraries that are not found under the typical install locations would result in linker errors, like /usr/bin/ld: cannot find -lmy-hacking-library-1.0. This solution fixes the linker error for that case.
Another issue could be that the pkg-config files are not installed in the normal place, and the pkg-config paths for the project need to be added using the PKG_CONFIG_PATH environment variable while cmake is running (see other Stack Overflow questions regarding this). This solution also works well when you use the correct pkg-config path.
Using IMPORTED_TARGET is key to solving the issues above. This solution is an improvement on this earlier answer and boils down to this final version of a working CMakeLists.txt:
cmake_minimum_required(VERSION 3.14)
project(ya-project C)
# the `pkg_check_modules` function is created with this call
find_package(PkgConfig REQUIRED)
# these calls create special `PkgConfig::<MODULE>` variables
pkg_check_modules(MY_PKG REQUIRED IMPORTED_TARGET any-package)
pkg_check_modules(YOUR_PKG REQUIRED IMPORTED_TARGET ya-package)
add_executable(program-name file.c ya.c)
target_link_libraries(program-name PUBLIC
PkgConfig::MY_PKG
PkgConfig::YOUR_PKG)
Note that target_link_libraries does more than change the linker commands. It also propagates other PUBLIC properties of specified targets like compiler flags, compiler defines, include paths, etc., so, use the PUBLIC keyword with caution.
It's rare that one would only need to link with SDL2. The currently popular answer uses pkg_search_module() which checks for given modules and uses the first working one.
It is more likely that you want to link with SDL2 and SDL2_Mixer and SDL2_TTF, etc... pkg_check_modules() checks for all the given modules.
# sdl2 linking variables
find_package(PkgConfig REQUIRED)
pkg_check_modules(SDL2 REQUIRED sdl2 SDL2_ttf SDL2_mixer SDL2_image)
# your app
file(GLOB SRC "my_app/*.c")
add_executable(my_app ${SRC})
target_link_libraries(my_app ${SDL2_LIBRARIES})
target_include_directories(my_app PUBLIC ${SDL2_INCLUDE_DIRS})
target_compile_options(my_app PUBLIC ${SDL2_CFLAGS_OTHER})
Disclaimer: I would have simply commented on Grumbel's self answer if I had enough street creds with stackoverflow.
Most of the available answers fail to configure the headers for the pkg-config library. After meditating on the Documentation for FindPkgConfig I came up with a solution that provides those also:
include(FindPkgConfig)
if(NOT PKG_CONFIG_FOUND)
message(FATAL_ERROR "pkg-config not found!" )
endif()
pkg_check_modules(<some-lib> REQUIRED IMPORTED_TARGET <some-lib>)
target_link_libraries(<my-target> PkgConfig::<some-lib>)
(Substitute your target in place of <my-target> and whatever library in place of <some-lib>, accordingly.)
The IMPORTED_TARGET option seems to be key and makes everything then available under the PkgConfig:: namespace. This was all that was required and also all that should be required.
There is no such command as target_use. But I know several projects that have written such a command for their internal use. But every project want to pass additional flags or defines, thus it does not make sense to have it in general CMake. Another reason not to have it are C++ templated libraries like Eigen, there is no library but you only have a bunch of include files.
The described way is often correct. It might differ for some libraries, then you'll have to add _LDFLAGS or _CFLAGS. One more reason for not having target_use. If it does not work for you, ask a new question specific about SDL2 or whatever library you want use.
If you are looking to add definitions from the library as well, the add_definitions instruction is there for that. Documentation can be found here, along with more ways to add compiler flags.
The following code snippet uses this instruction to add GTKGL to the project:
pkg_check_modules(GTKGL REQUIRED gtkglext-1.0)
include_directories(${GTKGL_INCLUDE_DIRS})
link_directories(${GTKGL_LIBRARY_DIRS})
add_definitions(${GTKGL_CFLAGS_OTHER})
set(LIBS ${LIBS} ${GTKGL_LIBRARIES})
target_link_libraries([insert name of program] ${LIBS})
I would like to compile the following C file on an embedded platform:
https://github.com/openwsn-berkeley/openwsn-fw/blob/develop/firmware/openos/bsp/chips/at86rf231/radio.c
However, as you can see, on lines 20-26 of radio.c it references "radiotimer_capture_cbt":
typedef struct {
radiotimer_capture_cbt startFrame_cb;
radiotimer_capture_cbt endFrame_cb;
radio_state_t state;
} radio_vars_t;
radio_vars_t radio_vars;
So now I need to hunt down where it is defined and make sure I include the right header.
I have cloned the entire GIT repository here: https://github.com/openwsn-berkeley/openwsn-fw, and I'm looking for a way to compile this easily.
Is there a better way to get this compiled other than going through the brutal dependency nightmare?
My ultimate goal is only to get radio.c compiled and anything it needs. I do not see any makefiles in this project so I'm expecting they want us to use an IDE.
The project seems to use scons as a build system. So the simplest way is to dive into the scons files.
There's a small scons file in the directory containing the linked file and two main script in the top directory.
But if you want to play, first remove headers include, try to compile (using -c) to know which one are really needed. Once you get an object file (.o) you can use nm to identify missing symbols (marked with U.) Good luck …
Suppose I would like to create a library A that links against another (system) library B of which the following files are installed:
$ ll /usr/lib/libB*
libB.so -> libB.so.3
libB.so.3 -> libB.so.3.0
libB.so.3.0
When creating my own libA.so*, I suppose it'd be good practice to include any of libB.so* on the link line. In fact, the linker flag -Wl,--no-undefined even enforces this.
It doesn't seem to make a difference which of the above libB files are used for linking since eventually they all point to the same file libB.so.3.0, but I'm guessing there are best practices for this, too.
What's recommended and why?
What's recommended and why?
Only linking against libB.so is officially supported. Linking against libB.so.3 or libB.so.3.0 works more or less by accident; don't do it.
You can read about external library versioning here.
I'm trying to adjust 3rd person code to my needs. This code is provided with CMake config files used to build and install it. There is possibility to choose one of libraries. And in code is often used #ifdef USE_FTD2XX directive. I saw that this is defined in CMamkeFiles.txt file like here:
option(USE_FTD2XX "Use FTDI libFTD2XX instead of free libftdi" ON)
if(USE_FTD2XX)
find_package(libFTD2XX)
endif(USE_FTD2XX)
if(LIBFTD2XX_FOUND)
include_directories(${LIBFTD2XX_INCLUDE_DIR})
add_definitions( -DUSE_FTD2XX )
else(LIBFTD2XX_FOUND)
set(LIBFTD2XX_LIBRARIES "")
endif(LIBFTD2XX_FOUND)
But if I simply use *.c and *.cpp files and I analyse and run it simply from IDE (Codeblocks), how could I set using this library in C++ code instead of in CMake? I'm also sure that I want use always this one so it can be fixed.
Should I simply #define USE_FTD2XX in main file?
You cannot simply #define USE_FTD2XX because you also need specific linker options for this to work (i.e. the library to link with). If the option is OFF in cmake, the specific link options won't be present in the Makefile and most likely you'll have linker errors.
So CMake takes care of everything automatically for you, but you need to re-generate your makefiles each time you want to toggle options on/off.
If only headers were involved and no library to link with (like some parts of the Boost framework), then yeah, defining USE_FTD2XX in your should be enough.
In my SConscript I have the following line:
Program("xtest", Split("main.cpp"), LIBS="mylib fltk Xft Xinerama Xext X11 m")
How do I get scons to use mylib.a instead of mylib.so, while linking dynamically with the other libraries?
EDIT: Looking to use as few platform specific hacks as possible.
Passing the full filepath wrapped in a File node will force static linking. For example:
lib = File('/usr/lib/libfoo.a')
Program('bar', 'main.c', LIBS = [lib])
Will produce the following linker command line
g++ -o bar main.o /usr/lib/libfoo.a
Notice how the "-l" flag is not passed to the linker for this LIBS entry. This effectively forces static linking. The alternative is to modify LINKFLAGS to get what you want with the caveat that you are bypassing the library dependency scanner -- the status of the library will not be checked for rebuilds.
To make this platform independent you append the env['SHLIBSUFFIX'] onto the library you want to use. env['SHLIBSUFFIX'] gives you this environments suffix for shared libraries.
You also have the ['SHLIBPREFIX'], ['LIBPREFIX'], ['LIBSUFFIX'] and ['PROGSUFFIX'], all useful for situations like this.
Edit:
I obviously haven't made myself understood, so I will clarify.
The return value of these lookups are strings to the pre/suffixes that platform uses. In that way you can refer to the file you need on each platform. Note that you cannot use it as a pure string, it has to be embedded as a file node as BennyG suggests. Working with nodes are anyway the best solution as file nodes are much more versatile than a string.
Hope this helps.