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Help: Add documentation for <target>_EXPORTS compile definition

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Fixes: #27554
This commit is contained in:
Ralf Habacker
2026-02-02 11:07:01 -05:00
committed by Brad King
parent e0702518d4
commit 3400248c1a
2 changed files with 19 additions and 10 deletions
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Help/manual/cmake-buildsystem.7.rst
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@@ -404,9 +404,14 @@ for compiling a target.
These are passed to the compiler with ``-D`` flags, or equivalent,
in an unspecified order.
The :prop_tgt:`DEFINE_SYMBOL` target property is also used
as a compile definition as a special convenience case for
``SHARED`` and ``MODULE`` library targets.
When compiling sources of a ``SHARED`` library, a ``MODULE`` library,
or an ``EXECUTABLE`` with :prop_tgt:`ENABLE_EXPORTS` enabled, CMake
automatically defines a target-specific preprocessor symbol.
By default the definition is of the form ``<target>_EXPORTS``, but it
can be overridden by the :prop_tgt:`DEFINE_SYMBOL` target property.
This allows headers to detect whether they are included from inside
their implementation sources, and to correctly set up export/import
annotations or visibility of symbols.
:prop_tgt:`COMPILE_OPTIONS`
List of compile options for compiling sources in the target.
Help/prop_tgt/DEFINE_SYMBOL.rst
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@@ -1,17 +1,21 @@
DEFINE_SYMBOL
-------------
Define a symbol when compiling this target's sources.
Define a preprocessor symbol when compiling this target's sources.
``DEFINE_SYMBOL`` sets the name of the preprocessor symbol defined when
compiling sources in a shared library. If not set here then it is set
to ``target_EXPORTS`` by default (with some substitutions if the target is
not a valid C identifier). This is useful for headers to know whether
they are being included from inside their library or outside to
properly setup dllexport/dllimport decorations on Windows.
CMake adds this definition when compiling sources of a ``SHARED`` library,
a ``MODULE`` library, or an ``EXECUTABLE`` with :prop_tgt:`ENABLE_EXPORTS`
enabled. If ``DEFINE_SYMBOL`` is not set, the default definition is of
the form ``<target>_EXPORTS`` (with some substitutions if the target is
not a valid C identifier).
The symbol is only defined while compiling the target itself and is not
propagated to dependent targets.
On POSIX platforms, this can optionally be used to control the visibility
of symbols.
CMake provides support for such decorations with the :module:`GenerateExportHeader`
module.
See also the ``COMPILE_DEFINITIONS`` under :ref:`Target Compile Properties`.