The Ultimate Guide to Telling CMake to Link to a Static Library Instead of a Shared One When Using find_package()

Are you tired of struggling with CMake’s default behavior of linking to shared libraries when you want to use static libraries instead? Do you find yourself searching for a solution online, only to end up with cryptic error messages and confusing documentation? Fear not, dear developer, for we’re about to embark on a thrilling adventure to tame the beast that is CMake and make it do our bidding!

What’s the Big Deal About Static Libraries Anyway?

Before we dive into the nitty-gritty of telling CMake to link to static libraries, let’s take a step back and understand why we might want to do so in the first place. Static libraries, as opposed to shared libraries, have some significant advantages:

• Faster Execution: Since the library is compiled into the executable, there’s no overhead of loading the library at runtime.
• Fewer Dependencies: Your application doesn’t rely on the library being present on the system, making deployment easier.
• Better Security: With the library compiled into the executable, it’s harder for attackers to intercept or modify the library.

Now that we’ve established the benefits of static libraries, let’s get to the meat of the matter: how do we tell CMake to link to them instead of shared libraries?

The find_package() Conundrum

The `find_package()` command is a powerful tool in CMake’s arsenal, allowing us to easily discover and link against external libraries. However, by default, it will always prefer linking to shared libraries over static ones. This is because shared libraries are, well, shared, and can be used by multiple applications simultaneously. But what if we want to use a static library instead?

The solution lies in the `find_package()` command’s optional `STATIC` keyword. Yes, you read that right – it’s as simple as adding `STATIC` to your `find_package()` call:

find_package(MyLibrary REQUIRED STATIC)

By adding the `STATIC` keyword, we’re telling CMake to look for a static version of the library instead of the shared one. But what if the static library doesn’t exist, or we want to fall back to the shared library if the static one can’t be found?

That’s where the `find_package()` command’s `NO_MODULE` and `REQUIRED` keywords come into play:

find_package(MyLibrary NO_MODULE REQUIRED STATIC)

The `NO_MODULE` keyword tells CMake to not use the module’s default behavior, which would normally try to find the shared library first. By combining it with the `STATIC` keyword, we’re effectively telling CMake to search for the static library exclusively.

But what if we want to provide a fallback option, just in case the static library can’t be found? That’s where the `REQUIRED` keyword comes in. By setting `REQUIRED` to `FALSE`, we can make the `find_package()` call optional, allowing CMake to fall back to the shared library if the static one can’t be found:

find_package(MyLibrary NO_MODULE REQUIRED_FALSE STATIC)

But Wait, There’s More! – Library Paths and File Naming Conventions

When using `find_package()` with the `STATIC` keyword, CMake will expect the static library to have a specific naming convention and be located in a specific directory. By default, CMake will look for the static library in the `lib/` directory and expect it to have a name like `libMyLibrary.a` (on Unix-like systems) or `MyLibrary.lib` (on Windows).

If your static library has a different naming convention or is located in a non-standard directory, you’ll need to tell CMake where to find it. You can do this using the `LIBRARY_DIRS` and `LIBRARY_NAMES` properties:

set(MyLibrary_LIBRARY_DIRS "/path/to/lib")
set(MyLibrary_LIBRARY_NAMES "mylibrary_static")

find_package(MyLibrary REQUIRED_STATIC)

In this example, we’re setting the `LIBRARY_DIRS` property to `/path/to/lib`, which tells CMake where to find the static library. We’re also setting the `LIBRARY_NAMES` property to `mylibrary_static`, which specifies the name of the static library file.

Putting it All Together – A Real-World Example

Let’s say we have a project that uses the popular zlib compression library, and we want to link against the static version of zlib instead of the shared one. Here’s an example CMakeLists.txt file that demonstrates how to achieve this:

cmake_minimum_required(VERSION 3.10)

project(MyProject)

set(CMAKE_CXX_STANDARD 14)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

find_package(zlib REQUIRED_STATIC)

if(zlib_FOUND)
  include_directories(${zlib_INCLUDE_DIRS})
  link_directories(${zlib_LIBRARY_DIRS})
  add_executable(myapp main.cpp)
  target_link_libraries(myapp ${zlib_LIBRARIES})
endif()

In this example, we’re using the `find_package()` command with the `STATIC` keyword to tell CMake to look for the static version of zlib. We’re also using the `CMAKE_CXX_STANDARD` and `CMAKE_CXX_STANDARD_REQUIRED` variables to set the C++ standard and require it, respectively.

We then include the zlib headers, link against the zlib library, and add an executable target called `myapp`. The `target_link_libraries()` function is used to link the `myapp` target against the zlib library.

Conclusion

Telling CMake to link to a static library instead of a shared one when using `find_package()` might seem like a daunting task, but with the right keywords and properties, it’s actually quite straightforward. By using the `STATIC` keyword, specifying library paths and file naming conventions, and providing fallback options, we can take control of CMake’s linking behavior and ensure that our projects use the right type of library for the job.

Remember, with great power comes great responsibility – use your newfound knowledge wisely, and may the linking gods smile upon your projects!

Keyword/Property	Description
`STATIC`	Tells CMake to look for a static version of the library instead of the shared one.
`NO_MODULE`	Tells CMake not to use the module’s default behavior, which would normally try to find the shared library first.
`REQUIRED`	Sets the `find_package()` call to be required or optional.
`LIBRARY_DIRS`	Sets the directory where CMake should look for the static library.
`LIBRARY_NAMES`	Sets the name of the static library file.

Now, go forth and conquer the world of CMake linking!

Frequently Asked Question

Get ready to master the art of telling CMake to link to a static library instead of a shared one when using find_package()!