Messages in this thread Patch in this message | ![/](/images/icornerl.gif) | | Date | Sun, 31 Dec 2006 15:13:59 -0500 (EST) | From | "Robert P. J. Day" <> | Subject | Re: [PATCH] Documentation: Explain a second alternative for multi-line macros. |
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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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