.BR _SVID_SOURCE .
.TP
.B _REENTRANT
-Defining this macro exposes definitions of certain reentrant functions.
-For multithreaded programs, use
-.I "cc\ \-pthread"
-instead.
+Historically,
+defining this macro exposed definitions of certain reentrant functions.
+However, already for many years this macro has had few effects,
+and since glibc 2.3, no effects that were not also achieved by defining
+.BR _POSIX_C_SOURCE
+with a value of 199606L or greater.
+This macro is now deprecated; since glibc 2.25,
+defining it has the same effect as defining
+.BR _POSIX_C_SOURCE
+with a value of 199606L or greater.
.TP
.B _THREAD_SAFE
-Synonym for
+Synonym for the (deprecated)
.BR _REENTRANT ,
provided for compatibility with some other implementations.
.TP