cmake with vcpkg on macOS cannot find header files

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04-09-2024

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Solving the "CMake with vcpkg on macOS cannot find header files" Issue

This article will delve into the common problem of CMake failing to find header files installed by vcpkg on macOS and provide a comprehensive solution.

We'll analyze the provided example, understand the root cause, and explore the recommended approach for seamless integration.

The Problem:

The error "fatal error: 'fmt/core.h' file not found" indicates that the CMake build process cannot locate the fmt/core.h header file. This typically arises from an incorrect configuration between CMake and vcpkg on macOS.

Understanding the Root Cause:

On Windows, vcpkg integrate install automatically modifies system environment variables and compiler settings to integrate vcpkg packages. However, this functionality is absent on macOS. This absence necessitates a manual approach to link vcpkg installations with your CMake projects.

The Solution:

The key lies in configuring CMake to correctly find the vcpkg-installed libraries and header files. Here's how to do it:

1. Ensure vcpkg Installation: Verify that you have installed vcpkg correctly and that fmt is installed via vcpkg install fmt.
2. Configure CMake to Use vcpkg:
   • Add a Custom CMake Toolchain File: Create a file named vcpkg.cmake in your project's root directory (or any preferred location). This file will guide CMake to find the vcpkg installation.
   • Content of vcpkg.cmake:

     set(CMAKE_TOOLCHAIN_FILE "${CMAKE_SOURCE_DIR}/vcpkg/scripts/buildsystems/vcpkg.cmake")
     set(CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}/vcpkg/scripts/buildsystems")
     include(${CMAKE_MODULE_PATH}/vcpkg.cmake)
     

   • Point CMake to vcpkg.cmake: When configuring your project with CMake, specify the path to your vcpkg.cmake file using -DCMAKE_TOOLCHAIN_FILE=path/to/vcpkg.cmake.
3. Update CMakeLists.txt: Make sure your CMakeLists.txt file correctly uses find_package(fmt REQUIRED), which will now locate fmt based on your vcpkg.cmake setup.
4. Rebuild: Run cmake . followed by make to rebuild your project.

Example Implementation:

Let's assume your vcpkg installation is at /Users/user/vcpkg and your project is in /Users/user/mylib:

• Create vcpkg.cmake in /Users/user/mylib:

  set(CMAKE_TOOLCHAIN_FILE "${CMAKE_SOURCE_DIR}/vcpkg/scripts/buildsystems/vcpkg.cmake")
  set(CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}/vcpkg/scripts/buildsystems")
  include(${CMAKE_MODULE_PATH}/vcpkg.cmake)
  

• Run CMake:

  cmake -B build -DCMAKE_TOOLCHAIN_FILE=./vcpkg.cmake -S .
  

• Build:

  make
  

Additional Tips:

• If you encounter errors after setting up the toolchain file, check your CMake version and make sure it is compatible with the vcpkg version.
• Use find_package(fmt CONFIG) if you are using vcpkg's "config mode" to ensure that CMake properly detects the installed library.

By following these steps, you'll successfully integrate vcpkg with CMake on macOS, enabling smooth compilation of projects that rely on vcpkg-installed packages.