Doc fix.

[gnulib.git] / lib / stdbool_.h

diff --git a/lib/stdbool_.h b/lib/stdbool_.h
index 69f6ef7..efa80ba 100644 (file)
--- a/lib/stdbool_.h
+++ b/lib/stdbool_.h
@@ -1,4 +1,4 @@
-/* Copyright (C) 2001-2002 Free Software Foundation, Inc.
+/* Copyright (C) 2001, 2002, 2003, 2006 Free Software Foundation, Inc.
    Written by Bruno Haible <haible@clisp.cons.org>, 2001.
 
    This program is free software; you can redistribute it and/or modify
@@ -13,29 +13,97 @@
 
    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software Foundation,
-   Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
+   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
 
 #ifndef _STDBOOL_H
 #define _STDBOOL_H
 
 /* ISO C 99 <stdbool.h> for platforms that lack it.  */
 
+/* Usage suggestions:
+
+   Programs that use <stdbool.h> should be aware of some limitations
+   and standards compliance issues.
+
+   Standards compliance:
+
+       - <stdbool.h> must be #included before 'bool', 'false', 'true'
+         can be used.
+
+       - You cannot assume that sizeof (bool) == 1.
+
+       - Programs should not undefine the macros bool, true, and false,
+         as C99 lists that as an "obsolescent feature".
+
+   Limitations of this substitute, when used in a C89 environment:
+
+       - <stdbool.h> must be #included before the '_Bool' type can be used.
+
+       - You cannot assume that _Bool is a typedef; it might be a macro.
+
+       - In C99, casts and automatic conversions to '_Bool' or 'bool' are
+         performed in such a way that every nonzero value gets converted
+         to 'true', and zero gets converted to 'false'.  This doesn't work
+         with this substitute.  With this substitute, only the values 0 and 1
+         give the expected result when converted to _Bool' or 'bool'.
+
+   Also, it is suggested that programs use 'bool' rather than '_Bool';
+   this isn't required, but 'bool' is more common.  */
+
+
 /* 7.16. Boolean type and values */
 
 /* BeOS <sys/socket.h> already #defines false 0, true 1.  We use the same
    definitions below, but temporarily we have to #undef them.  */
 #ifdef __BEOS__
+# include <OS.h> /* defines bool but not _Bool */
 # undef false
 # undef true
 #endif
 
-/* For the sake of symbolic names in gdb, define _Bool as an enum type.  */
-#ifndef __cplusplus
+/* For the sake of symbolic names in gdb, we define true and false as
+   enum constants, not only as macros.
+   It is tempting to write
+      typedef enum { false = 0, true = 1 } _Bool;
+   so that gdb prints values of type 'bool' symbolically. But if we do
+   this, values of type '_Bool' may promote to 'int' or 'unsigned int'
+   (see ISO C 99 6.7.2.2.(4)); however, '_Bool' must promote to 'int'
+   (see ISO C 99 6.3.1.1.(2)).  So we add a negative value to the
+   enum; this ensures that '_Bool' promotes to 'int'.  */
+#if defined __cplusplus || defined __BEOS__
+  /* A compiler known to have 'bool'.  */
+  /* If the compiler already has both 'bool' and '_Bool', we can assume they
+     are the same types.  */
 # if !@HAVE__BOOL@
-typedef enum { false = 0, true = 1 } _Bool;
+typedef bool _Bool;
 # endif
 #else
-typedef bool _Bool;
+# if !defined __GNUC__
+   /* If @HAVE__BOOL@:
+        Some HP-UX cc and AIX IBM C compiler versions have compiler bugs when
+        the built-in _Bool type is used.  See
+          http://gcc.gnu.org/ml/gcc-patches/2003-12/msg02303.html
+          http://lists.gnu.org/archive/html/bug-coreutils/2005-11/msg00161.html
+          http://lists.gnu.org/archive/html/bug-coreutils/2005-10/msg00086.html
+        Similar bugs are likely with other compilers as well; this file
+        wouldn't be used if <stdbool.h> was working.
+        So we override the _Bool type.
+      If !@HAVE__BOOL@:
+        Need to define _Bool ourselves. As 'signed char' or as an enum type?
+        Use of a typedef, with SunPRO C, leads to a stupid
+          "warning: _Bool is a keyword in ISO C99".
+        Use of an enum type, with IRIX cc, leads to a stupid
+          "warning(1185): enumerated type mixed with another type".
+        The only benefit of the enum type, debuggability, is not important
+        with these compilers.  So use 'signed char' and no typedef.  */
+#  define _Bool signed char
+enum { false = 0, true = 1 };
+# else
+   /* With this compiler, trust the _Bool type if the compiler has it.  */
+#  if !@HAVE__BOOL@
+typedef enum { _Bool_must_promote_to_int = -1, false = 0, true = 1 } _Bool;
+#  endif
+# endif
 #endif
 #define bool _Bool