Improve ARRAY_SIZE macro.

[paraslash.git] / para.h

diff --git a/para.h b/para.h
index 1dcbb6d32a134db962abe7eb4e2a457c53d7f3fe..c30e4710ee7ff9b2d725dee06b7ec4a378e1c820 100644 (file)
--- a/para.h
+++ b/para.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 1997-2010 Andre Noll <maan@systemlinux.org>
+ * Copyright (C) 1997-2011 Andre Noll <maan@systemlinux.org>
  *
  * Licensed under the GPL v2. For licencing details see COPYING.
  */
@@ -70,7 +70,7 @@
 /** Version text used by various commands if -V switch was given. */
 #define VERSION_TEXT(prefix) "para_" prefix " " PACKAGE_VERSION \
        " (" GIT_VERSION ": " CODENAME ")" "\n" \
-       "Copyright (C) 2010 Andre Noll\n" \
+       "Copyright (C) 2011 Andre Noll\n" \
        "This is free software with ABSOLUTELY NO WARRANTY." \
        " See COPYING for details.\n" \
        "Written by Andre Noll.\n" \
@@ -170,8 +170,23 @@ _static_inline_ long int para_random(unsigned max)
        typeof(y) _divisor = y; \
        ((x) + _divisor - 1) / _divisor; })
 
+/**
+ * Assert a build-time dependency, as an expression.
+ *
+ * \param cond The compile-time condition which must be true.
+ *
+ * Compilation will fail if the condition isn't true, or can't be evaluated by
+ * the compiler. This can be used in an expression: its value is "0".
+ *
+ * Taken from ccan.
+ */
+#define EXPR_BUILD_ASSERT(cond) (sizeof(char [1 - 2 * !(cond)]) - 1)
+
+/* &a[0] degrades to a pointer: a different type from an array */
+#define _array_size_chk(arr) EXPR_BUILD_ASSERT(\
+       !__builtin_types_compatible_p(typeof(arr), typeof(&(arr)[0])))
 /** Get the size of an array */
-#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]) + _array_size_chk(arr))
 
 /**
  * Wrapper for isspace.