From: Andre Noll <maan@systemlinux.org>
Date: Fri, 4 Feb 2011 06:46:28 +0000 (+0100)
Subject: Improve ARRAY_SIZE macro.
X-Git-Tag: v0.4.6~18^2
X-Git-Url: http://git.tuebingen.mpg.de/?p=paraslash.git;a=commitdiff_plain;h=b908fa3f5577d1f64bd8628d03a344aee2ca6fa1;ds=sidebyside

Improve ARRAY_SIZE macro.

Compilation now fails if the given argument not an array but a pointer.

Idea taken from ccan. Thanks Rusty!
---

diff --git a/gcc-compat.h b/gcc-compat.h
index ffd714f7..45d9c9ba 100644
--- a/gcc-compat.h
+++ b/gcc-compat.h
@@ -23,3 +23,4 @@
 # endif
 
 #define _static_inline_ static inline
+
diff --git a/para.h b/para.h
index c5e12fe6..c30e4710 100644
--- a/para.h
+++ b/para.h
@@ -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.