How to use external DLLs in CMake project - c++

I've been searching over the internet but I couldn't find anything that would answer my question (or I don't know what to search for).
Anyway here's my issue:
I want to use 3rdParty libraries (.dll files) in my CMake project. Library (https://github.com/pitzer/SiftGPU) that I want to include is open source and is also available in binary which I would like to use and also uses CMake as build tool if that's relevant.
I hope I was clear enough.

First, edit your CMakeLists.txt to include your third party library. You'll need two thing: path to header files and library file to link to. For instance:
# searching for include directory
find_path(SIFTGPU_INCLUDE_DIR siftgpu.h)
# searching for library file
find_library(SIFTGPU_LIBRARY siftgpu)
if (SIFTGPU_INCLUDE_DIR AND SIFTGPU_LIBRARY)
# you may need that if further action in your CMakeLists.txt depends
# on detecting your library
set(SIFTGPU_FOUND TRUE)
# you may need that if you want to conditionally compile some parts
# of your code depending on library availability
add_definitions(-DHAVE_LIBSIFTGPU=1)
# those two, you really need
include_directories(${SIFTGPU_INCLUDE_DIR})
set(YOUR_LIBRARIES ${YOUR_LIBRARIES} ${SIFTGPU_LIBRARY})
endif ()
Next, you can do the same for other libraries and when every libraries are detected, link to the target:
target_link_libraries(yourtarget ${YOUR_LIBRARIES})
Then you can configure your project with CMake, but as it doesn't have any magic way to find your installed library, it won't find anything, but it'll create two cache variables: SIFTGPU_INCLUDE_DIR and SIFTGPU_LIBRARY.
Use the CMake GUI to have SIFTGPU_INCLUDE_DIR pointing to the directory containing the header files and SIFTGPU_LIBRARY to the .lib file of your third party library.
Repeat for every third party library, configure again and compile.

Related

How to use cmake to check if some libraries exists before build our sources?

Usually, open source packages will have cmake to check if some headers or libraries exists or not, I wish my own project has this same functionality.
So I wish to know if cmake provides some command to check if some ".so"/".a"/".h" files exists in the current linux system or not, if not cmake will give me some hint to install them?
How does cmake support this?
Usually one would use the find_package(ABC REQUIRED) and then refer to it in your project. This will ensure that the dependent library is installed and cmake will fail if it is not.
You can find lot's of example on how this works in your cmake installation, for example C:\Program Files\CMake\share\cmake-3.13\Modules\FindZLIB.cmake will search for the zlib library by looking in the file system for normal places where this library would be installed and if it finds it will set these variables accordingly:
# ZLIB_INCLUDE_DIRS - where to find zlib.h, etc.
# ZLIB_LIBRARIES - List of libraries when using zlib.
# ZLIB_FOUND - True if zlib found.
To achieve this header files are found using the cmake command find_path, and libraries (static and shared) are found using find_library.
To search for arbitrary library you can use find_library() command. Same task for headers is accomplished by find_file(). You can also search for executables with find_program().
As #Damian said in his naswer, many libraries provide "config" files, like FindBoost.cmake. Such libraries can be found by calling find_package(Boost) command. This command would locate and load config file and set corresponding variables.
You need to provide -config.cmake files to tell other projects where your libraries and headers are. Here, you will found what are you looking for.

How can I set cmake to look in different places for the headers and libraries

The project I'm working on is migrating everything over to cmake, but has a structure for how the library and include files for external libraries are stored. Is there any way to have cmake look in one place for the includes, and another for the library files? We are using 'find_package' to search.
find_package does exactly what the name suggest, search for a package, which usually is a set of headers and library files. The packages you search for may have different structures, but usually the find module search for a specific one, for example /lib for the libraries and /usr/include for the headers.
If you already know where to look for the headers or for the libraries you can set them with
include_directories()
link_directories()
It is also possible to set include and link per target with
target_include_directories()
target_link_libraries()
Maybe;
include_directories(...) for include folders
link_directories(...) for folders with libraries
There's also the target_include_directories(...) if you want more specific control.

CMake: target_include_directories() prints an error when I try to add the source directory itself, or one of its subdirectories

I am writing a C++ library (header-only) and am using CMake to generate my (Visual Studio) project and solution files. I'm also writing a test suite, which is part of the same CMake project.
My problem occurs when I call target_include_directories() on the target that represents my header-only library, so that consumers of my library may find its header files. I get the following error message (even though generation is NOT aborted).
CMake Error in CMakeLists.txt:
Target "Fonts" INTERFACE_INCLUDE_DIRECTORIES property contains path:
"D:/Projects/GPC/fonts/include"
which is prefixed in the source directory.
(D:/Projects/GPC/Fonts being the top-level directory of my library project. Btw the problem remains if I move my header files to the top directory.)
The offending line in my CMakeLists.txt is this (adapted for simplicity):
target_include_directories(Fonts INTERFACE "${CMAKE_CURRENT_SOURCE_DIR}/include")
I do not understand what I'm doing wrong. Without target_include_directories(), code of consumer projects simply can't include my header files (unless in installed form, but I haven't gotten to that yet, and in any case I want to be able to use my library from its build tree, without installation.)
I feel like I'm missing something basic here; yet I've searched for hours without finding a solution or explanation.
The origin of the problem is not the target_include_directories command itself, but the attempt to install a target that has a public or interface include directory prefixed in the source path (i.e. the include directory is a subdirectory of your ${PROJECT_SOURCE_DIR}.)
While it is perfectly fine and desirable to use absolute paths when building the library from scratch, a third party library that pulls in a prebuilt version of that library will probably want to use a different include path. After all, you do not want all of your users to mirror the directory structure of your build machine, just to end up in the right include path.
CMake's packaging mechanism provides support for both of these use cases: You may pull in a library directly from the build tree (that is, check out the source, build it, and point find_package() to the directory), or from an install directory (run make INSTALL to copy built stuff to the install directory and point find_package() to that directory). The latter approach needs to be relocatable (that is, I build and install on my machine, send you the resulting directory and you will be able to use it on your machine from a different directory structure), while the former is not.
This is a very neat feature, but you have to account for it when setting up the include directories. Quoting the manual for target_include_directories:
Include directories usage requirements commonly differ between the
build-tree and the install-tree. The BUILD_INTERFACE and
INSTALL_INTERFACE generator expressions can be used to describe
separate usage requirements based on the usage location. Relative
paths are allowed within the INSTALL_INTERFACE expression and are
interpreted relative to the installation prefix. For example:
target_include_directories(mylib PUBLIC
$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include/mylib>
$<INSTALL_INTERFACE:include/mylib> # <prefix>/include/mylib
)
The BUILD_INTERFACE and INSTALL_INTERFACE generator expressions do all the magic:
$<INSTALL_INTERFACE:...>
Content of ... when the property is exported using install(EXPORT), and empty otherwise.
$<BUILD_INTERFACE:...>
Content of ... when the property is exported using export(), or when the target is used by another target in the same buildsystem.
Expands to the empty string otherwise.

Including Shared Libraries (.so) with CMake

I've been trying to include different types of libraries with CMake.
.a
.dylib
.so
I finally, got both the .a and .dylib to work with this code.
find_library(libname NAMES libcef.dylib PATHS ${libname_PATH})
along with this, underneath where I add_executable to initialize all my files for the build.
target_link_libraries(${PROJECT_NAME} ${libname})
However, I tried using the same code on a .so file and it doesn't seem to work.
I get this statement from cmake when I try building.
Target "project name" links to item
-- path of file --
which is a full-path but not a valid library file name.
I'm not sure if this is the correct way to handle .so files or perhaps I'm not even fully understanding what an .so file is. Any input and/or clarification would be much appreciated.
edit:
THEORY- my theory is because it doesn't have a lib in front of the name of the library name its called ffmpegsumo.so. However, when i try renaming it the file name still saves into the variable name very strange.
The same should work with .so files also, just make sure the required .so file is present at ${libname_PATH} which you have given.
find_library treats all types (.a / .so/ .dylib/ .dll) the same way. Problem may be the following
-- path not set up correctly
-- error because of absolute path
-- .so not present
-- If the error is from build (not from configure only) the .so might be corrupt, try replacing it
--Your library does not seem to be valid
Shared libraries are linked dynamically. That means that your OS will automatically look for and load the .so files when the time comes to run the application. You only need to tell cmake the name of the library and the OS will take care of the rest.
For example, if you want to link to the dynamic library for libSDL.so, you just say: target_link_libraries(${PROJECT_NAME} SDL)
As a sanity check, your linker will look to make sure that the SDL library does exist on your computer. That's why you might get a linking error if that library is not available at link-time, even if it's really a dynamic library.

Including my own shared library with cmake

I have the following code in my CMakeLists.txt for finding my shared library libsieve.so
set(CPPLIB_DIR "${CMAKE_SOURCE_DIR}/../core/build")
find_library(CPPLIB_SIEVE_LIBRARY NAMES libsieve PATHS CPPLIB_DIR)
But it fails and won't find my library. I have the following directory structure:
core
build: libsieve.so
project: CMakeLists.txt
What am I doing wrong?
I don't know why cmake doesn't find the needed library but I can suggest a way to make it happen with the help cmake-gui: if the first run of "configure" fails to find the library you can point it to the needed library manually (set the full absolute path). Most of the time such solution works for me.
Also if the library was built with one tool chain (say, Intel C++) and you project is being built with another tool chain (say, clang) the failure to find the library may be due to binary incompatibility between the project and the library.
Upd. The original problem was referencing CPPLIB_DIR. It should have been:
find_library(CPPLIB_SIEVE_LIBRARY NAMES sieve PATHS ${CPPLIB_DIR})
Cmake find_library expect you to provide the library name or the library file name.
You mixed the two by adding a "lib" prefix to your library name. So you should try to replace libsieve by either sieve or libsieve.so.