* Makefile.in (timevar.o): Depend on flags.h.

[pf3gnuchains/gcc-fork.git] / gcc / cpp.texi

diff --git a/gcc/cpp.texi b/gcc/cpp.texi
index 0d2b2ee..700d637 100644 (file)
--- a/gcc/cpp.texi
+++ b/gcc/cpp.texi
@@ -138,6 +138,7 @@ and this may cause problems with other languages.
 
 @node Global Actions, Directives, Top, Top
 @section Transformations Made Globally
+@cindex ASCII NUL handling
 
 Most C preprocessor features are inactive unless you give specific directives
 to request their use.  (Preprocessing directives are lines starting with
@@ -214,6 +215,43 @@ This exception is relevant only if you use the @samp{-trigraphs}
 option to enable trigraph processing.  @xref{Invocation}.
 @end itemize
 
+The preprocessor handles null characters embedded in the input file
+depending upon the context in which the null appears.  Note that here we
+are referring not to the two-character escape sequence "\0", but to the
+single character ASCII NUL.
+
+There are three different contexts in which a null character may
+appear:-
+
+@itemize @bullet
+@item
+Within comments.  Here, null characters are silently ignored.
+
+@item
+Within a string or character constant.  Here the preprocessor emits a
+warning, but preserves the null character and passes it through to the
+output file.
+
+@item
+In any other context, the preprocessor issues a warning, and discards
+the null character.  In all other respects the preprocessor treats it
+like whitespace, combining it with any surrounding whitespace to become
+a single whitespace token.  Representing the null character by "^@@",
+this means that code like
+
+@example
+#define X^@@1
+@end example
+
+is equivalent to
+
+@example
+#define X 1
+@end example
+
+and X is defined with replacement text "1".
+@end itemize
+
 @node Directives, Header Files, Global Actions, Top
 @section Preprocessing Directives
 
@@ -998,10 +1036,11 @@ C++.
 
 @item __cplusplus 
 @findex __cplusplus 
-The draft ANSI standard for C++ used to require predefining this
-variable.  Though it is no longer required, GNU C++ continues to define
-it, as do other popular C++ compilers.  You can use @samp{__cplusplus}
-to test whether a header is compiled by a C compiler or a C++ compiler.
+The ISO standard for C++ requires predefining this variable.  You can
+use @samp{__cplusplus} to test whether a header is compiled by a C
+compiler or a C++ compiler. The compiler currently uses a value of
+@samp{1}, instead of the value @samp{199711L}, which would indicate
+full conformance with the standard.
 
 @item __STRICT_ANSI__
 @findex __STRICT_ANSI__