# CheckSymbolExists

Provides a macro to check if a symbol exists as a function, variable, or macro in `C`.

`check_symbol_exists`

      check_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. `<variable>` will be created as an internal cache variable.

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 (so intrinsics may not be detected). If the symbol is a type, enum value, or intrinsic it will not be recognized (consider using `CheckTypeSize` or `CheckCSourceCompiles`). If the check needs to be done in C++, consider using `CheckCXXSymbolExists` instead.

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`
  a ;-list of macros to define (-DFOO=bar).
`CMAKE_REQUIRED_INCLUDES`
  a ;-list of header search paths to pass to the compiler.
`CMAKE_REQUIRED_LINK_OPTIONS`
  a ;-list of options to add to the link command.
`CMAKE_REQUIRED_LIBRARIES`
  a ;-list of libraries to add to the link command. See policy `CMP0075`.
`CMAKE_REQUIRED_QUIET`
  execute quietly without messages.