C_STANDARD
----------

.. versionadded:: 3.1

The C standard whose features are requested to build this target.

This property specifies the C standard whose features are requested
to build this target.  For some compilers, this results in adding a
flag such as ``-std=gnu11`` to the compile line.  For compilers that
have no notion of a C standard level, such as Microsoft Visual C++ before
VS 16.7, this property has no effect.

Supported values are:

``90``
  C89/C90

``99``
  C99

``11``
  C11

``17``
  .. versionadded:: 3.21

  C17

``23``
  .. versionadded:: 3.21

  C23

If the value requested does not result in a compile flag being added for
the compiler in use, a previous standard flag will be added instead.  This
means that using:

.. code-block:: cmake

  set_property(TARGET tgt PROPERTY C_STANDARD 11)

with a compiler which does not support ``-std=gnu11`` or an equivalent
flag will not result in an error or warning, but will instead add the
``-std=gnu99`` or ``-std=gnu90`` flag if supported.  This "decay" behavior may
be controlled with the :prop_tgt:`C_STANDARD_REQUIRED` target property.
Additionally, the :prop_tgt:`C_EXTENSIONS` target property may be used to
control whether compiler-specific extensions are enabled on a per-target basis.

See the :manual:`cmake-compile-features(7)` manual for information on
compile features and a list of supported compilers.

This property is initialized by the value of
the :variable:`CMAKE_C_STANDARD` variable if it is set when a target
is created.