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Date: Thu, 28 Jul 2011 04:25:08 -0400
From: pete <pfiland@mindspring.com>
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Subject: Re: is there anything unstandard in the c part here
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.c:8799

Willem wrote:
> 
> Ike Naar wrote:
> ) To be fair, the preferred idiom also relies on duplication: in
> )
> )     p = malloc(n * sizeof *p);
> )
> ) the duplication is benign, but if the pointer expression
> ) becomes more complicated, as in
> )
> )     *(*co_matrix)[pivot] = malloc(n * sizeof **(*co_matrix)[pivot]);
> )
> ) the duplication becomes a bit of a nuisance.
> ) Because of the duplicated complexity, a silly mistake like
> )
> )     *(*co_matrix)[pivot] = malloc(n * sizeof *(*co_matrix)[pivot]);
> )
> ) may creep in, which is not caught by the compiler, and is easily
> ) overlooked during code inspection.
> )
> ) Also, if the pointer expression has side effects:
> )
> )     a[j++] = malloc(n * sizeof *a[j++]);
> )
> ) although the preferred idiom works okay here (thanks to the fact that
> ) sizeof does not evaluate its operand), this may confuse the reader.
> 
> Which is why god invented macros.
> 
> #define NEW(x,n) ((x)=malloc((n) * sizeof(x)))
> 
> (If I remember correctly)

ITYM 
#define NEW(x, n) ((x) = malloc((n) * sizeof *(x)))

-- 
pete