How to Link an External Library With Cmake?

To link an external library with CMake, you need to use the target_link_libraries() function in your CMakeLists.txt file. This function allows you to specify the target (executable or library) that requires the external library, as well as the name of the external library to link.

You can either specify the absolute path to the library file, or use CMake's find_package() function to locate the library automatically. If you choose to use find_package(), you will need to include the necessary find module for the library in your CMakeLists.txt file.

Once you have specified the external library to link, you can generate the build files using CMake and build your project as usual. CMake will take care of including the necessary flags and paths to link the external library with your target executable or library.

How to specify compiler flags when linking an external library with CMake?

To specify compiler flags when linking an external library with CMake, you can use the target_link_libraries command along with the INTERFACE, PUBLIC, or PRIVATE keywords to specify the scope of the compiler flags.

Here's an example of how you can specify compiler flags when linking an external library with CMake:

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# Find the library (e.g., Boost)
find_package(Boost REQUIRED)

# Create a target for your executable
add_executable(my_executable main.cpp)

# Link the external library to your executable
target_link_libraries(my_executable PRIVATE Boost::boost)

# Specify compiler flags for the external library
target_compile_options(my_executable PRIVATE "-Wall -Wextra")

In this example, we specify the Boost library as an external library and link it to the my_executable target using the target_link_libraries command. We then use the target_compile_options command to specify the compiler flags -Wall -Wextra for the my_executable target.

By using the PRIVATE keyword with target_compile_options, we ensure that these compiler flags are only applied to the my_executable target and not to any other targets that may also link to the Boost library.

How to link a third-party library that includes its own CMake configuration file?

To link a third-party library that includes its own CMake configuration file, you can use the add_subdirectory command in your CMakeLists.txt file to include the library's CMake configuration.

Here's an example of how you can link a third-party library called "example_library" that has its own CMake configuration file included in its repository:

1. Clone the third-party library repository into your project's directory:

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git clone https://github.com/example/example_library.git

1. In your project's CMakeLists.txt file, add the following line to include the library's CMake configuration:

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add_subdirectory(example_library)

1. After adding the add_subdirectory command, you can use the library in your project by linking it to your target as follows:

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target_link_libraries(your_target_name example_library)

1. Finally, configure and build your project using CMake as usual:

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mkdir build
cd build
cmake ..
make

By following these steps, you should be able to successfully link the third-party library that includes its own CMake configuration file to your project.

What is the difference between a required and optional dependency when specifying library dependencies in CMake?

In CMake, a required dependency means that the specified library is necessary for building the project and will result in a build failure if it is not found. On the other hand, an optional dependency means that the specified library is not necessary for building the project and the build process will continue even if it is not found.

When specifying library dependencies in CMake, you can use the find_package command to locate and import external libraries into your project. By default, find_package searches for required dependencies, but you can also specify optional dependencies using the OPTIONAL keyword.

For required dependencies, you would use the following syntax:

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find_package(MyLibrary REQUIRED)

For optional dependencies, you would use the following syntax:

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find_package(MyOptionalLibrary OPTIONAL)

In both cases, CMake will provide variables that you can use to link against the libraries in your project. However, if a required dependency is not found, the build will fail, whereas if an optional dependency is not found, the build will proceed without it.

What is the difference between a public and private dependency when linking libraries in CMake?

In CMake, a public dependency means that both the target library itself and any targets linking to it will also have access to the public includes and compile definitions of the dependency. This means that the headers and compile options provided by the dependency are "exported" to other targets.

On the other hand, a private dependency means that only the target library itself will have access to the includes and compile definitions of the dependency, and any targets linking to it will not have access to those resources.

In simple terms, using public dependencies makes the dependency's headers and compile options available to the targets that link to the target library, while using private dependencies restricts access to those resources only to the target library itself.

How to link a library that is not installed system-wide with CMake?

To link a library that is not installed system-wide with CMake, you can use the target_link_libraries() command in your CMakeLists.txt file. Here is an example of how you can link a library called mylibrary that is located in the libs directory of your project:

1. Specify the include directory for the library in your CMakeLists.txt file:

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include_directories(${CMAKE_SOURCE_DIR}/libs/mylibrary/include)

1. Add the library to your project as an external target:

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add_subdirectory(libs/mylibrary)

1. Finally, link the library to your target executable:

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target_link_libraries(your_target_name PRIVATE mylibrary)

By following these steps, you should be able to link a library that is not installed system-wide using CMake.

How to link a header-only library in CMake?

To link a header-only library in CMake, you can add the library as an INTERFACE target in your CMakeLists.txt file. Here's an example of how you can do this:

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# Include the header-only library in your project
add_library(header_only_library INTERFACE)

# Add the include directory of the library
target_include_directories(header_only_library INTERFACE /path/to/header_only_library)

# Link your target with the header-only library
target_link_libraries(your_target PRIVATE header_only_library)

Replace /path/to/header_only_library with the path to the directory containing the header files of the library.

After adding the above code to your CMakeLists.txt file, CMake will automatically handle the linking of the header-only library when building your project.