* mktime.c (not_equal_tm): Remove redundant check.

[gnulib.git] / lib / stdbool_.h

diff --git a/lib/stdbool_.h b/lib/stdbool_.h
index 69f6ef7..e33715a 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 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
@@ -20,19 +20,65 @@
 
 /* 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__)
 # if !@HAVE__BOOL@
-typedef enum { false = 0, true = 1 } _Bool;
+#  if defined __SUNPRO_C && (__SUNPRO_C < 0x550 || __STDC__ == 1)
+    /* Avoid stupid "warning: _Bool is a keyword in ISO C99".  */
+#   define _Bool signed char
+enum { false = 0, true = 1 };
+#  else
+typedef enum { _Bool_must_promote_to_int = -1, false = 0, true = 1 } _Bool;
+#  endif
 # endif
 #else
 typedef bool _Bool;