cmake header-only library specify name

Yulia Chive

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07-12-2024

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Creating and managing header-only libraries with CMake can be straightforward, but specifying the library's name requires careful attention to detail. This article will guide you through the process, clarifying potential pitfalls and providing best practices. The key is understanding how CMake distinguishes between the library's target name (internal to CMake) and its actual name as it's presented to consumers (e.g., in #include directives).

Understanding the Problem: Target vs. Installation Name

CMake operates with targets, which represent build artifacts like executables and libraries. When dealing with a header-only library, you don't have a compiled .a or .so file. Instead, you're managing a collection of header files. The challenge lies in properly naming this target within CMake and ensuring that the installed headers are organized logically and easily accessible.

The crucial distinction is between the target name (used internally by CMake) and the installation name (how the library is presented to users). Often, these are the same, but understanding their differences is critical for managing complex projects.

Method 1: Using install(TARGETS) (Recommended)

This is the cleanest and most recommended approach. It uses CMake's install(TARGETS) command to explicitly define how the header files are installed, decoupling the target name from the installation name (which is what matters to users).

# CMakeLists.txt for a header-only library

add_library(MyHeaderOnlyLib INTERFACE) # Define an INTERFACE library

# Add your header files
target_include_directories(MyHeaderOnlyLib PUBLIC
    {{content}}lt;BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
    {{content}}lt;INSTALL_INTERFACE:${CMAKE_INSTALL_PREFIX}/include/MyHeaderOnlyLib>
)

# Install the headers.  Note the "DESTINATION" argument!
install(TARGETS MyHeaderOnlyLib DESTINATION include/MyHeaderOnlyLib)

In this example:

• add_library(MyHeaderOnlyLib INTERFACE) creates an interface library target. This is crucial for header-only libraries because it signals that there's no compiled code.
• target_include_directories specifies the include directories. <BUILD_INTERFACE> points to the headers during the build, and <INSTALL_INTERFACE> sets the install location.
• install(TARGETS) installs the headers. DESTINATION include/MyHeaderOnlyLib dictates the installation path, defining the library's accessible name for users. Users will then #include "MyHeaderOnlyLib/header.h" (assuming header.h is in the MyHeaderOnlyLib directory).

Method 2: Manual Installation with install(FILES) (Less Recommended)

This method provides more direct control but requires more manual work and can be error-prone, especially in larger projects.

# CMakeLists.txt

# ... (other CMake commands) ...

install(FILES
    ${CMAKE_CURRENT_SOURCE_DIR}/include/myheader.h
    DESTINATION include/MyHeaderOnlyLib
)

This approach is less desirable because it doesn't leverage CMake's target management capabilities. It's prone to errors if you forget to update the install(FILES) command when adding or removing header files.

Choosing the Right Method

The install(TARGETS) approach is strongly recommended. It provides:

• Better maintainability: Changes to the header files are automatically handled by CMake.
• Improved organization: Libraries are installed in a consistent and predictable manner.
• Enhanced integration: Works seamlessly with CMake's target-based dependency management.

The manual install(FILES) method should only be considered for very simple scenarios where the overhead of using install(TARGETS) is deemed unnecessary.

Using the Library

Once your header-only library is installed, users can include it in their projects using:

#include "MyHeaderOnlyLib/header.h" // Adjust the path as needed

This path reflects the DESTINATION argument in your install(TARGETS) command.

By understanding the distinction between the CMake target and the installation name, and by using the recommended install(TARGETS) method, you can ensure your header-only library is well-organized, easy to use, and maintainable. Remember to always prioritize clarity and consistency in your CMake scripts for better project management and collaboration.