pitrou commented on code in PR #35924:
URL: https://github.com/apache/arrow/pull/35924#discussion_r1234963044
##########
docs/source/developers/cpp/building.rst:
##########
@@ -254,6 +254,34 @@ Several build types are possible:
* ``Release``: applies compiler optimizations and removes debug information
from the binary.
+.. note::
+
+ These built types provide suitable optimization/debug flags by
+ default but you can change them by specifying
+ ``-DARROW_C_FLAGS_${BUILD_TYPE}=...`` and/or
+ ``-DARROW_CXX_FLAGS_${BUILD_TYPE}=...``. ``${BUILD_TYPE}`` is upper
+ case of build type. For example, ``DEBUG``
+ (``-DARROW_C_FLAGS_DEBUG=...`` / ``-DARROW_CXX_FLAGS_DEBUG=...``) for the
+ ``Debug`` build type and ``RELWITHDEBINFO``
+ (``-DARROW_C_FLAGS_RELWITHDEBINFO=...`` /
+ ``-DARROW_CXX_FLAGS_RELWITHDEBINFO=...``) for the ``RelWithDebInfo``
+ build type.
+
+ For example, you can use ``-O3`` as an optimization flag by
+ specifying ``-DARROW_CXX_FLAGS_RELEASE=-O3`` for the ``Release``
+ build type. You can use ``-g3`` as a debug flag by specifying
+ ``-DARROW_CXX_FLAGS_DEBUG=-g3`` for the ``Debug`` build type.
+
+ You can also use the standard ``-DCMAKE_C_FLAGS_${BUILD_TYPE}=...``
+ and ``-DCMAKE_CXX_FLAGS_${BUILD_TYPE}=...`` style but
+ ``-DARROW_C_FLAGS_${BUILD_TYPE`` and
+ ``-DARROW_CXX_FLAGS_${BUILD_TYPE}=...`` style is
+ recommended. Because ``-DCMAKE_C_FLAGS_${BUILD_TYPE}=...`` and
+ ``-DCMAKE_CXX_FLAGS_${BUILD_TYPE}=...`` style replaces all default
+ flags provided by CMake. ``-DARROW_C_FLAGS_${BUILD_TYPE`` and
+ ``-DARROW_CXX_FLAGS_${BUILD_TYPE}=...`` style just overrides the
+ default flags specified instead of replacing them.
Review Comment:
```suggestion
the ``ARROW_C_FLAGS_${BUILD_TYPE}`` and
``ARROW_CXX_FLAGS_${BUILD_TYPE}`` variables are
recommended. The ``CMAKE_C_FLAGS_${BUILD_TYPE}`` and
``CMAKE_CXX_FLAGS_${BUILD_TYPE}`` variables replace all default
flags provided by CMake, while ``ARROW_C_FLAGS_${BUILD_TYPE}`` and
``ARROW_CXX_FLAGS_${BUILD_TYPE}`` just append the
flags specified, which allows selectively overriding some of the defaults.
```
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