A few small additions

diff --git a/man7/ftm.7 b/man7/ftm.7
index ce63c11534009ca97907d1f25dce3468dac1255a..f3991e8cf2f8429bfd6e00e8558b4eebb01dcc0d 100644 (file)
--- a/man7/ftm.7
+++ b/man7/ftm.7
@@ -81,7 +81,7 @@ is defined, then expose definitions corresponding to the XPG4v2
 UNIX extensions.
 .TP
 .B _ISOC99_SOURCE
-Exposes C 99 extensions to IOC C (1990).
+Exposes C 99 extensions to ISO C (1990).
 .TP
 .B _LARGEFILE64_SOURCE
 Expose definitions for the alternative API specified by the 
@@ -119,6 +119,25 @@ and
 .BR _XOPEN_SOURCE
 with the value 600.
 In addition, various GNU-specific extensions are also exposed.
+.PP
+When
+.BR gcc (1)
+is invoked, then the following macros are defined by default:
+.BR _BSD_SOURCE ,
+.BR _SVID_SOURCE ,
+.BR _POSIX_SOURCE ,
+and
+.BR POSIX_C_SOURCE =199506.
+If individual macros are defined, then other macros are disabled
+unless they are also explicitly defined.  (Exception:
+if 
+.BR POSIX_C_SOURCE
+is not otherwise defined, 
+then it is always defined with the value 199506,
+unless the compiler is invoked in one of is standard modes, e.g., the
+.I -std=c99
+flag.)
+Multiple macros can be defined; the results are additive.
 .SH CONFORMING TO
 POSIX.1 specifies
 .BR _POSIX_C_SOURCE ,
@@ -142,4 +161,3 @@ Other systems have an analogous file, but typically with a different name.
 This header file is automatically included by other header files as 
 required: it is not necessary to explicitly include it in order to 
 employ feature test macros.
-.SH "SEE ALSO"