target_link_libraries with code examples

As a software developer, you are likely familiar with the importance of libraries when it comes to building great software. Libraries are collections of pre-written code that solve common problems so that developers can focus on the unique aspects of their projects. However, using libraries effectively can be a difficult and complicated process. That's where the CMake command target_link_libraries comes in.

At its core, target_link_libraries is a CMake command that allows a developer to specify which libraries should be linked to a particular target. The target can be an executable, a shared library, or a static library. This command is one of the most important and useful aspects of CMake, as it enables developers to easily manage library dependencies and integrate third-party libraries into their projects.

In this article, we will explore target_link_libraries in detail. We will start with a brief overview of how libraries work in CMake, and then we will dive into the specifics of target_link_libraries. Along the way, we'll provide practical examples to demonstrate how this command can be used effectively in real-world projects.

Libraries in CMake

Before we dive into target_link_libraries specifically, let's first take a look at how libraries work in CMake.

CMake is a build system generator, meaning it is responsible for generating Makefiles, Ninja files, Visual Studio projects, etc. that implement the build process for your project. When you specify the libraries that your project needs, CMake generates the necessary build files to link those libraries to your project.

In CMake, a library can be either a static library or a shared library. A static library is a collection of object files that are linked directly into your executable. This means that all of the code in the static library will be included in your final executable at build time. On the other hand, a shared library is a collection of object files that are compiled separately and linked dynamically at runtime. Shared libraries are loaded into memory when they are needed by your program, and they can be shared by multiple processes on the system.

Libraries in CMake are specified using the add_library command. This command creates a new library and adds it to the build system. The add_library command takes three parameters:

add_library(library_name [STATIC | SHARED] source_files)

The library_name parameter specifies the name of the library you are creating. The second parameter specifies whether the library is a static or shared library. Finally, the source_files parameter specifies the source files that will be included in the library.

Here is an example of how to create a static library in CMake:

add_library(mylib STATIC source1.cpp source2.cpp source3.cpp)

This command creates a library called mylib and includes the source files source1.cpp, source2.cpp, and source3.cpp. When CMake generates the build files for this library, it will create a single object file that contains all of the code in these source files.

Here is an example of how to create a shared library in CMake:

add_library(mylib SHARED source1.cpp source2.cpp source3.cpp)

This command creates a shared library called mylib and includes the same source files as before. However, because this is a shared library, CMake generates a different object file for each source file. Additionally, it generates a shared library file (.so file on Linux, .dll file on Windows) that contains all of these object files.

Now that we have a basic understanding of libraries in CMake, let's move on to target_link_libraries.

target_link_libraries

The target_link_libraries command is used to specify the libraries that a particular target should link to. The target parameter can be either an executable, a shared library, or a static library.

The syntax of the target_link_libraries command is as follows:

target_link_libraries(target_name [INTERFACE] [PRIVATE] [PUBLIC] library_name1 [library_name2 …])

The target_name parameter specifies the name of the target you want to link libraries to. The library_name parameters specify the names of the libraries you want to link. You can specify multiple libraries by separating their names with spaces.

There are three different keywords that you can use before the library names: INTERFACE, PRIVATE, and PUBLIC. These keywords control how the library is linked to the target and its dependencies.

• PUBLIC: The library is linked to the target, and any targets that depend on this target will also link to the library.
• PRIVATE: The library is linked to the target, but any targets that depend on this target will not link to the library.
• INTERFACE: The library is not linked to the target, but any targets that depend on this target will link to the library. This is useful when creating libraries that provide an API but do not implement the functionality themselves.

Here is an example of how to use target_link_libraries to link a static library to an executable:

add_library(mylib STATIC source1.cpp source2.cpp source3.cpp)
add_executable(myexe main.cpp)
target_link_libraries(myexe PRIVATE mylib)

In this example, we first create a static library called mylib using the add_library command. We then create an executable called myexe using the add_executable command. Finally, we use target_link_libraries to link the mylib library to the myexe executable.

Here is an example of how to use target_link_libraries to link a shared library to a static library:

add_library(mylib SHARED source1.cpp source2.cpp source3.cpp)
add_library(myotherlib STATIC other.cpp)
target_link_libraries(myotherlib PRIVATE mylib)

In this example, we create a shared library called mylib using the add_library command. We then create a static library called myotherlib using the same command, but with different source files. Finally, we use target_link_libraries to link the mylib library to the myotherlib library.

Conclusion

In conclusion, target_link_libraries is an essential command in CMake that enables developers to easily manage library dependencies and integrate third-party libraries into their projects. By following the syntax and usage examples provided above, developers can efficiently link their libraries to executable and library targets. This results in more manageable and maintainable code, which makes for a better overall development experience.

Libraries are a crucial part of software development. They save developers time, effort, and resources because they provide pre-written and tested code for common tasks. However, using libraries effectively can be a daunting task. That's where CMake and its target_link_libraries command come in.

CMake is a cross-platform build system generator that enables developers to manage complex builds across different environments. It allows developers to write a single script that can be used to build projects across different platforms. CMake's target_link_libraries command enables developers to link their libraries to different targets, including executables, shared libraries, and static libraries.

When using target_link_libraries, developers need to specify the target to which the libraries should be linked. This target can be either an executable, a shared library, or a static library. Developers also need to specify the name of the library or libraries to be linked and any other necessary flags.

The three different flags that target_link_libraries provides—PUBLIC, PRIVATE, and INTERFACE—allow developers to control how libraries are linked. PUBLIC specifies that the library will be linked to the target and any targets that depend on that target. PRIVATE specifies that the library will be linked only to the target. INTERFACE specifies that the library will not be linked to the target but will be linked to any targets that depend on the target.

Here are some examples of how target_link_libraries can be applied:

1. Linking an executable to a static library:

add_library(mylib STATIC source1.cpp source2.cpp source3.cpp)
add_executable(myexe main.cpp)
target_link_libraries(myexe PRIVATE mylib)

Here, the add_library command creates a static library called mylib with three source files: source1.cpp, source2.cpp, and source3.cpp. The add_executable command creates an executable called myexe and the target_link_libraries command links myexe to mylib.

2. Linking a shared library to a executable:

add_library(mylib SHARED source1.cpp source2.cpp source3.cpp)
add_executable(myexe main.cpp)
target_link_libraries(myexe PRIVATE mylib)

Here, the add_library command creates a shared library called mylib with three source files: source1.cpp, source2.cpp, and source3.cpp. The add_executable command creates an executable called myexe, and the target_link_libraries command links myexe to mylib.

3. Linking a shared library to a static library:

add_library(mylib SHARED source1.cpp source2.cpp source3.cpp)
add_library(myotherlib STATIC other.cpp)
target_link_libraries(myotherlib PRIVATE mylib)

Here, the add_library command creates a shared library called mylib with three source files: source1.cpp, source2.cpp, and source3.cpp. The add_library command also creates a static library called myotherlib with one source file: other.cpp. The target_link_libraries command links myotherlib to mylib.

In conclusion, target_link_libraries is a powerful command in CMake that enables developers to manage library dependencies and integrate third-party libraries into their projects. Proper use of target_link_libraries can improve the overall development experience by creating more manageable and maintainable code.

Popular questions

1. What is target_link_libraries in CMake?
   Answer: target_link_libraries is a CMake command that links libraries to a particular target, including executables, shared libraries, or static libraries.

2. What are the three flags available in target_link_libraries?
   Answer: PUBLIC, PRIVATE, and INTERFACE are the three flags available in target_link_libraries. PUBLIC links the library to the target and its dependencies; PRIVATE links the library only to the target, and INTERFACE links the library to any targets that depend on the target.

3. What is the purpose of add_library and add_executable commands in CMake?
   Answer: The add_library command creates a library, either a static library or a shared library, and adds it to the build system. The add_executable command creates an executable and adds it to the build system.

4. How can we use target_link_libraries to link a shared library to an executable?
   Answer: Here is an example of how we can use target_link_libraries to link a shared library to an executable in CMake:

add_library(mylib SHARED source1.cpp source2.cpp source3.cpp)
add_executable(myexe main.cpp)
target_link_libraries(myexe PRIVATE mylib)

5. How does target_link_libraries help to manage libraries in CMake?
   Answer: target_link_libraries helps to manage libraries in CMake by allowing developers to specify which libraries should be linked to particular targets. This command simplifies the process of managing library dependencies and integrating third-party libraries into projects.

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