On Sun, 31 Dec 2006, Muli Ben-Yehuda wrote:
> On Sun, Dec 31, 2006 at 02:49:48PM -0500, Robert P. J. Day wrote:
>
> > there would appear to be *lots* of cases where the ({ }) notation
> > is used when nothing is being returned. i'm not sure you can be
> > that adamant about that distinction at this point.
>
> IMHO, the main point of CodingStyle is to clarify how new code
> should be written and old code should've been written.
ok, how about this as a patch:
diff --git a/Documentation/CodingStyle b/Documentation/CodingStyle
index 9069189..064a13e 100644
--- a/Documentation/CodingStyle
+++ b/Documentation/CodingStyle
@@ -549,13 +549,26 @@ may be named in lower case.
Generally, inline functions are preferable to macros resembling functions.
-Macros with multiple statements should be enclosed in a do - while block:
-
-#define macrofun(a, b, c) \
- do { \
- if (a == 5) \
- do_this(b, c); \
- } while (0)
+There are two techniques for defining macros that contain multiple
+statements, depending on whether you're returning a value or not:
+
+ (a) If there is no return value from the macro, you should enclose
+ the statements in a do - while block, as in:
+
+ #define macrofun(a, b, c) \
+ do { \
+ if (a == 5) \
+ do_this(b, c); \
+ } while (0)
+
+ (b) If the macro is designed to return a value, you should use the
+ gcc extension that a compound statement enclosed in parentheses
+ represents an expression, as in:
+
+ #define maxint(a, b) ({ \
+ int _a = (a), _b = (b); \
+ _a > _b ? _a : _b; \
+ })
Things to avoid when using macros:
-
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