Improve ARRAY_SIZE macro.

[paraslash.git] / para.h

diff --git a/para.h b/para.h
index c5e12fe6da3ef864bdc16bb0eaa178a8b5965cee..c30e4710ee7ff9b2d725dee06b7ec4a378e1c820 100644 (file)
--- 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.