add section on C23doc/manual/R-exts.texi

git-svn-id: https://svn.r-project.org/R/trunk@87656 00db46b3-68df-0310-9c12-caf00c1e9a41

doc/NEWS.Rd

@@ -281,6 +281,20 @@
       \item The deprecated and seemingly never-used S-compatibility
       macros \code{F77_COM} and \code{F77_COMDECL} have been removed
       from header \file{R_ext/RS.h}.
+
+      \item Header \file{R_ext/Rboolean.h} now defines the type
+      \code{Rboolean} as an alias of the standard C type \code{bool}.
+
+      Currently this is done from C (not C++) only if
+      \code{__bool_true_false_are_defined} is defined, which it is in
+      C23 mode or if the C99 header \file{stdbool.h} is included.
+      
+      Before release \file{stdbool.h} will be included from C if C23 mode is
+      not supported, and C++ \code{bool} will be used if called from
+      C++.
+
+      The macro \code{_R_RBOOLEAN_IS_BOOL_} is defined where
+      \code{Rboolean} is implemented \emph{via} \code{bool}.
     }
   }
 
@@ -603,10 +617,6 @@
       \item \code{as.roman(x)} now should work platform independently,
       also for, e.g., \code{x = "IIIII"} (= V) and \code{x = "IIIIII"}
       (= VI).
-
-      \item \command{R CMD Rd2pdf} works again on an installed package
-      directory containing \LaTeX help (from option \option{--latex}),
-      thanks to a report by \I{Peter Ruckdeschel}.
     }
   }
 }

doc/manual/R-exts.texi

@@ -6569,6 +6569,51 @@ Another build for Windows which may be sufficiently compatible with
 @uref{https://github.com/mstorsjo/llvm-mingw}: this uses @code{libc++}.
 
 
+@node C23 changes
+@subsubsection C23 changes
+
+Thw C23 standard was finally published in Oct 2024, by which time had
+been widely implemented for a least a couple of years.  It will become
+the default on GCC 15, and @R{} will use default to it if available from @R{}
+4.5.0.
+
+Some of the more significant changes are
+@c https://en.cppreference.com/w/c/23
+
+@itemize
+
+@item
+@code{bool}, @code{true} and @code{false} become keywords and so can no
+longer be used as identifiers.
+
+These have been available as a boolean type since C99 by including the
+header @file{stdbool.h}.  Both that and C23@footnote{but C23 declares
+that header and the macro to be obsolescent.} set the macro
+@code{__bool_true_false_are_defined} to @code{1} so this type can be
+used in all versions of C supported by @R{}.
+
+@item
+The meaning of an empty argument list has been changed to mean zero
+arguments --- however for clarity @code{fun(void)} is still preferred by
+many code readers and supported by all C standards.  (Compilers may warn
+about an empty argument list in C23 mode.)
+
+@item
+@code{INIINITY} and @code{NAN} are available via
+header @file{float.h} and deprecated in @file{math.h}.
+
+@item
+POSIC functions @code{memccpy}, @code{strdup} and @code{strndup} are
+part of C23.
+
+@item
+There are decimal floating-point types and functions and extended
+support of binary floating-point functions, including binary
+floating-point constants.
+@end itemize
+
+
+
 @node Portable Fortran code
 @subsection Portable Fortran code
 

src/include/R_ext/Boolean.h

@@ -1,6 +1,6 @@
 /*
  *  R : A Computer Language for Statistical Data Analysis
- *  Copyright (C) 2000, 2001 The R Core Team.
+ *  Copyright (C) 2000, 2025 The R Core Team.
  *
  *  This header file is free software; you can redistribute it and/or modify
  *  it under the terms of the GNU Lesser General Public License as published by
@@ -29,13 +29,56 @@
 #undef FALSE
 #undef TRUE
 
+/* This can eventually be simplified to
+#if (!defined __cplusplus) && !(defined __STDC_VERSION__ && __STDC_VERSION__ > 201710L)
+# include <stdbool.h>
+#endif
+
 #ifdef  __cplusplus
 extern "C" {
+typedef bool Rboolean;
+#define FALSE false
+#define TRUE true
+}
+#define _R_RBOOLEAN_IS_BOOL_ 1
 #endif
-typedef enum { FALSE = 0, TRUE /*, MAYBE */ } Rboolean;
+*/
 
 #ifdef  __cplusplus
+
+extern "C" {
+    /* once cp11 is soerted
+typedef bool Rboolean;
+#define FALSE false
+#define TRUE true
+    */
+typedef enum { FALSE = 0, TRUE } Rboolean;
 }
+
+# else
+
+// Also include standard C boolean type
+#if defined __STDC_VERSION__ && __STDC_VERSION__ > 201710L
+// C23 so these are keywords
+#else
+// stdbool.h is C99, so available everywhere
+//# include <stdbool.h>
 #endif
 
+/* 
+   __bool_true_false_are_defined is defined in stdbool.h, and C23, but
+   it and stdbool.h are declared obsolescent in C23.
+*/
+#ifdef __bool_true_false_are_defined
+typedef bool Rboolean;
+# define FALSE false
+# define TRUE true
+# define _R_RBOOLEAN_IS_BOOL_ 1
+#else
+typedef enum { FALSE = 0, TRUE } Rboolean;
+#endif //__bool_true_false_are_defined
+
+# endif // __cplusplus
+
+
 #endif /* R_EXT_BOOLEAN_H_ */