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# Distributed under the OSI-approved BSD 3-Clause License. See accompanying
# file Copyright.txt or for details.
Check if a symbol exists as a function, variable, or macro in ``C++``.
.. command:: check_cxx_symbol_exists
.. code-block:: cmake
check_cxx_symbol_exists(<symbol> <files> <variable>)
Check that the ``<symbol>`` is available after including given header
``<files>`` and store the result in a ``<variable>``. Specify the list of
files in one argument as a semicolon-separated list.
``check_cxx_symbol_exists()`` can be used to check for symbols as seen by
the C++ compiler, as opposed to :command:`check_symbol_exists`, which always
uses the ``C`` compiler.
If the header files define the symbol as a macro it is considered
available and assumed to work. If the header files declare the symbol
as a function or variable then the symbol must also be available for
linking. If the symbol is a type, enum value, or C++ template it will
not be recognized: consider using the :module:`CheckTypeSize`
or :module:`CheckCXXSourceCompiles` module instead.
.. note::
This command is unreliable when ``<symbol>`` is (potentially) an overloaded
function. Since there is no reliable way to predict whether a given function
in the system environment may be defined as an overloaded function or may be
an overloaded function on other systems or will become so in the future, it
is generally advised to use the :module:`CheckCXXSourceCompiles` module for
checking any function symbol (unless somehow you surely know the checked
function is not overloaded on other systems or will not be so in the
The following variables may be set before calling this macro to modify
the way the check is run:
string of compile command line flags.
a :ref:`;-list <CMake Language Lists>` of macros to define (-DFOO=bar).
a :ref:`;-list <CMake Language Lists>` of header search paths to pass to
the compiler.
a :ref:`;-list <CMake Language Lists>` of options to add to the link command.
a :ref:`;-list <CMake Language Lists>` of libraries to add to the link
command. See policy :policy:`CMP0075`.
execute quietly without messages.
For example:
.. code-block:: cmake
# Check for macro SEEK_SET
check_cxx_symbol_exists(SEEK_SET "cstdio" HAVE_SEEK_SET)
# Check for function std::fopen
check_cxx_symbol_exists(std::fopen "cstdio" HAVE_STD_FOPEN)