FE_DFL_ENV

From cppreference.com
< c‎ | numeric‎ | fenv
Defined in header <fenv.h>
#define FE_DFL_ENV  /*implementation defined*/
(since C99)

The macro constant FE_DFL_ENV expands to an expression of type const fenv_t*, which points to a full copy of the default floating-point environment, that is, the environment as loaded at program startup.

Additional macros that begin with FE_ followed by uppercase letters, and have the type const fenv_t*, may be supported by an implementation.