# How to Link Against the MulleObjC-startup Library in Your Project > Effortlessly link against the MulleObjC-startup library in your project. Discover simple dependency management with mulle-sde or manual CMake integration for seamless setup. - Repository: [mulle-objc/mulleobjc-startup](https://github.com/mulle-objc/mulleobjc-startup) - Tags: how-to-guide - Published: 2026-03-07 --- **To link against the MulleObjC-startup library, either use `mulle-sde add github:mulle-objc/MulleObjC-startup` for automatic dependency management, or manually configure CMake to include the library subdirectory and link the `MulleObjC-startup` target to your executable.** The `mulle-objc/mulleobjc-startup` repository provides a static library that supplies the essential `__register_mulle_objc_universe` entry point and automatically pulls in required runtime dependencies including `mulle-atinit` and `mulle-atexit`. Linking this library is mandatory for any executable that needs to bootstrap the Mulle Objective-C runtime. This guide covers both automated and manual integration methods. ## Using mulle‑sde to Link MulleObjC‑startup The **mulle‑sde** build tool offers the simplest way to integrate the library, automatically handling include paths, compiler flags, and link targets. ### Adding the Dependency Run the following command in your project root to fetch and link the library: ```bash mulle-sde add github:mulle-objc/MulleObjC-startup ``` This command retrieves the source code, updates your build configuration, and inserts the `-lMulleObjC-startup` link flag. After adding the dependency, build and run your project normally: ```bash mulle-sde run ``` The tool ensures that the static library and its transitive dependencies are correctly linked without manual CMake editing. ## Manual CMake Integration For projects requiring explicit control over the build system, you can manually add the library as a CMake subdirectory. ### Adding the Library Subdirectory First, clone the repository or add it as a git submodule, then reference it in your [`CMakeLists.txt`](https://github.com/mulle-objc/mulleobjc-startup/blob/main/CMakeLists.txt): ```cmake cmake_minimum_required(VERSION 3.13) project(MyApp LANGUAGES C) # Add the startup library source tree add_subdirectory(path/to/MulleObjC-startup) ``` The [`CMakeLists.txt`](https://github.com/mulle-objc/mulleobjc-startup/blob/main/CMakeLists.txt) in the library root defines the static target using the `Library` macro provided in `cmake/share/Library.cmake`. ### Linking the Target Connect the startup library to your executable and ensure headers are discoverable: ```cmake add_executable(${PROJECT_NAME} main.c) # Link the static startup library target_link_libraries(${PROJECT_NAME} PUBLIC MulleObjC-startup) # Include the public headers target_include_directories(${PROJECT_NAME} PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/path/to/MulleObjC-startup/include ) ``` This configuration imports the implementation from `src/MulleObjC-startup.m`, which contains the `__register_mulle_objc_universe` function that bootstraps the Objective-C universe. ## Required Headers and Implementation Details Regardless of the integration method, source files that interact with the startup routine must import the public header: ```c #import ``` The library exports the `__register_mulle_objc_universe` symbol defined in `src/MulleObjC-startup.m`, which initializes the runtime environment. The build definition in [`CMakeLists.txt`](https://github.com/mulle-objc/mulleobjc-startup/blob/main/CMakeLists.txt) uses `cmake/share/Library.cmake` to create the compile and link targets properly. When using **mulle‑sde**, these includes are configured automatically. In manual setups, verify that `path/to/MulleObjC-startup/include` is in your compiler's search path. ## Summary - **MulleObjC-startup** is a static library that provides the `__register_mulle_objc_universe` entry point required to bootstrap the Mulle Objective-C runtime. - Use `mulle-sde add github:mulle-objc/MulleObjC-startup` for automatic linking and header configuration. - For manual CMake integration, use `add_subdirectory` followed by `target_link_libraries(your_exe PUBLIC MulleObjC-startup)`. - Include `` in source files that need access to the startup routine. - The implementation resides in `src/MulleObjC-startup.m`, with build logic defined in the root [`CMakeLists.txt`](https://github.com/mulle-objc/mulleobjc-startup/blob/main/CMakeLists.txt) and `cmake/share/Library.cmake`. ## Frequently Asked Questions ### What is the purpose of the MulleObjC-startup library? The library provides the `__register_mulle_objc_universe` function that initializes the Objective-C runtime universe. It also links against `mulle-atinit` and `mulle-atexit` to handle constructor and destructor priorities, ensuring the runtime is ready before your application code executes. ### Can I use MulleObjC-startup with build systems other than CMake? While the repository is optimized for CMake and **mulle‑sde**, you can adapt the build logic for other systems. The critical requirement is compiling `src/MulleObjC-startup.m` and linking the resulting static library with your executable, then ensuring the header path `include/` is available to the compiler. ### Why does my executable fail to link without MulleObjC-startup? The Mulle Objective-C runtime requires a specific entry point to register the universe before `main()` executes. Without linking against `MulleObjC-startup`, the `__register_mulle_objc_universe` symbol remains undefined, causing linker errors or runtime crashes when attempting to send Objective-C messages. ### Where are the public headers located in the repository? The public interface is located at [`include/MulleObjC-startup/MulleObjC-startup.h`](https://github.com/mulle-objc/mulleobjc-startup/blob/main/include/MulleObjC-startup/MulleObjC-startup.h) in the source tree. When using **mulle‑sde**, this path is added to your include search paths automatically. For manual CMake setups, you must explicitly add the `include` directory to your target's include directories.