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    DateSun, 31 Dec 2006 15:13:59 -0500 (EST)
    From"Robert P. J. Day" <>
    SubjectRe: [PATCH] Documentation: Explain a second alternative for multi-line macros.
    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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