如何通过CMakeLists.txt配置构建文件输出至指定构建目录？

Great question! Let's break down how to replicate the behavior of your CLI command (cmake -DCMAKE_BUILD_TYPE=Debug -Bbuild -S./directory) directly within your CMakeLists.txt—though there's one key caveat we need to cover first.

First, a Critical Note #

The -B flag in your CLI command specifies the build directory where CMake generates all its build files. This is an external configuration set when you run the cmake command, and CMakeLists.txt can't directly define this build directory (since CMake needs to read the CMakeLists.txt before it knows where to generate build files). That said, we can add several configurations to simulate and enforce the behavior you want:

1. Set Default Build Type to Debug (Equivalent to -DCMAKE_BUILD_TYPE=Debug) #

If you want Debug to be the default build type when users don't specify it via the CLI, add this to your CMakeLists.txt:

# Set default build type to Debug if not specified
if(NOT CMAKE_BUILD_TYPE)
    set(CMAKE_BUILD_TYPE "Debug" CACHE STRING "Choose the build type." FORCE)
    # Optional: List valid build type options for the user
    set_property(CACHE CMAKE_BUILD_TYPE PROPERTY STRINGS "Debug" "Release" "RelWithDebInfo" "MinSizeRel")
endif()

Now, if someone runs cmake -S./directory -Bbuild without the -DCMAKE_BUILD_TYPE flag, CMake will automatically use the Debug configuration.

2. Enforce External Builds (Guide Users to Use a build Directory) #

To prevent users from accidentally running CMake directly in your source directory (which creates messy in-source builds), add this check:

# Block in-source builds
if(CMAKE_SOURCE_DIR STREQUAL CMAKE_BINARY_DIR)
    message(FATAL_ERROR "In-source builds are not allowed! Please create a dedicated build directory first, like:\nmkdir build && cd build && cmake ..")
endif()

This will throw an error if someone tries to run cmake in your source folder, pushing them to use a build directory just like your original CLI command specifies.

3. Control Where Build Artifacts Are Saved #

If you want to ensure your compiled binaries/libraries end up in consistent subfolders within the build directory (like build/bin or build/lib), add these lines:

# Set output directories for build artifacts
set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)  # For executables
set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib)  # For shared libraries
set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib)  # For static libraries

This ensures no matter where the build directory is, your output files will follow a clean structure matching what you'd get with -Bbuild.

Wrap-Up #

While you can't directly set the build directory (-B) from CMakeLists.txt, combining these three configurations will replicate the intent of your original CLI command: defaulting to Debug builds, guiding users to use a dedicated build folder, and organizing build artifacts neatly.

内容的提问来源于stack exchange，提问作者stunicks