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Help/manual: Update header-only library example

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Use target_sources with a named file set for the header-only library
example in cmake-buildsystem7.

Issue: #23400
This commit is contained in:
Martin Duffy
2022-04-22 10:33:10 -04:00
parent de802fc5a3
commit 4b25a0d512
1 changed files with 26 additions and 25 deletions
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51
Help/manual/cmake-buildsystem.7.rst
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@@ -1040,24 +1040,26 @@ Additionally, IDEs will show the source files as part of the target for
interactive reading and editing.
A primary use-case for ``INTERFACE`` libraries is header-only libraries.
Since CMake 3.23, header files may be associated with a library by adding
them to a header set using the :command:`target_sources` command:
.. code-block:: cmake
add_library(Eigen INTERFACE
src/eigen.h
src/vector.h
src/matrix.h
)
target_include_directories(Eigen INTERFACE
$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/src>
$<INSTALL_INTERFACE:include/Eigen>
add_library(Eigen INTERFACE)
target_sources(Eigen INTERFACE
FILE_SET HEADERS
BASE_DIRS src
FILES src/eigen.h src/vector.h src/matrix.h
)
add_executable(exe1 exe1.cpp)
target_link_libraries(exe1 Eigen)
Here, the usage requirements from the ``Eigen`` target are consumed and used
when compiling, but it has no effect on linking.
When we specify the ``FILE_SET`` here, the ``BASE_DIRS`` we define automatically
become include directories in the usage requirements for the target ``Eigen``.
The usage requirements from the target are consumed and used when compiling, but
have no effect on linking.
Another use-case is to employ an entirely target-focussed design for usage
requirements:
@@ -1081,26 +1083,25 @@ This way, the build specification of ``exe1`` is expressed entirely as linked
targets, and the complexity of compiler-specific flags is encapsulated in an
``INTERFACE`` library target.
``INTERFACE`` libraries may be installed and exported. Any content they refer
to must be installed separately:
``INTERFACE`` libraries may be installed and exported. We can install the
default header set along with the target:
.. code-block:: cmake
set(Eigen_headers
src/eigen.h
src/vector.h
src/matrix.h
)
add_library(Eigen INTERFACE ${Eigen_headers})
target_include_directories(Eigen INTERFACE
$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/src>
$<INSTALL_INTERFACE:include/Eigen>
add_library(Eigen INTERFACE)
target_sources(Eigen INTERFACE
FILE_SET HEADERS
BASE_DIRS src
FILES src/eigen.h src/vector.h src/matrix.h
)
install(TARGETS Eigen EXPORT eigenExport)
install(TARGETS Eigen EXPORT eigenExport
FILE_SET HEADERS DESTINATION include/Eigen)
install(EXPORT eigenExport NAMESPACE Upstream::
DESTINATION lib/cmake/Eigen
)
install(FILES ${Eigen_headers}
DESTINATION include/Eigen
)
Here, the headers defined in the header set are installed to ``include/Eigen``.
The install destination automatically becomes an include directory that is a
usage requirement for consumers.