Messages in this thread Patch in this message | | | Date | Sun, 31 Dec 2006 14:32:25 -0500 (EST) | From | "Robert P. J. Day" <> | Subject | [PATCH] Documentation: Explain a second alternative for multi-line macros. |
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Add an explanation for defining multi-line macros using the ({ }) notation to CodingStyle.
Signed-off-by: Robert P. J. Day <rpjday@mindspring.com>
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diff --git a/Documentation/CodingStyle b/Documentation/CodingStyle index 9069189..1d0ddb8 100644 --- a/Documentation/CodingStyle +++ b/Documentation/CodingStyle @@ -549,13 +549,24 @@ 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: +There are two techniques for defining macros that contain multiple +statements.
-#define macrofun(a, b, c) \ - do { \ + (a) Enclose those statements in a do - while block: + + #define macrofun(a, b, c) \ + do { \ + if (a == 5) \ + do_this(b, c); \ + } while (0) + + (b) Use the gcc extension that a compound statement enclosed in + parentheses represents an expression: + + #define macrofun(a, b, c) ({ \ if (a == 5) \ do_this(b, c); \ - } while (0) + })
Things to avoid when using macros:
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