# CheckVariableExists

Check if the variable exists.

`CHECK_VARIABLE_EXISTS`

      CHECK_VARIABLE_EXISTS(VAR VARIABLE)

      VAR      - the name of the variable
      VARIABLE - variable to store the result
                 Will be created as an internal cache variable.

  This macro is only for `C` variables.

The following variables may be set before calling this macro to modify the way the check is run:

`CMAKE_REQUIRED_FLAGS`

  string of compile command line flags.

`CMAKE_REQUIRED_DEFINITIONS`

  list of macros to define (-DFOO=bar).

`CMAKE_REQUIRED_LINK_OPTIONS`

  New in version 3.14: list of options to pass to link command.

`CMAKE_REQUIRED_LIBRARIES`

  list of libraries to link.

`CMAKE_REQUIRED_QUIET`

  New in version 3.1: execute quietly without messages.