The attached documentation-only patch clarifies the description
of the -dM option to mention that __FILE__ (and other predefined
macros) do no appear on the list generated by the option.
Martin
PR preprocessor/41540 - -dM -E doesn't #define __FILE__
gcc/ChangeLog:
PR preprocessor/41540
* doc/cppopts.texi (-dM): Update.
diff --git a/gcc/doc/cppopts.texi b/gcc/doc/cppopts.texi
index 0497712..bc76809 100644
--- a/gcc/doc/cppopts.texi
+++ b/gcc/doc/cppopts.texi
@@ -481,10 +481,10 @@ conflicts, the result is undefined.
@item -dM
@opindex dM
Instead of the normal output, generate a list of @samp{#define}
-directives for all the macros defined during the execution of the
-preprocessor, including predefined macros. This gives you a way of
-finding out what is predefined in your version of the preprocessor.
-Assuming you have no file @file{foo.h}, the command
+directives for macros defined during the execution of the preprocessor,
+including most predefined macros. This gives you a way of finding out
+what is predefined in your version of the preprocessor. Assuming you
+have no file @file{foo.h}, the command
@smallexample
touch foo.h; cpp -dM foo.h
@@ -493,6 +493,10 @@ touch foo.h; cpp -dM foo.h
@noindent
shows all the predefined macros.
+The predefined macros @code{__FILE__}, @code{__LINE__}, @code{__DATE__},
+and @code{__TIME__} are excluded from this list because their replacements
+may change from one line of output to the next.
+
@ifclear cppmanual
If you use @option{-dM} without the @option{-E} option, @option{-dM} is
interpreted as a synonym for @option{-fdump-rtl-mach}.
