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Re: which one is faster?

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echo ma <fatmck@gmail.com> writes:
> on a 32bit system.
>
> #pragma pack(4)
> struct TestStruct
> {
> 	unsigned short a;
> 	unsigned short b;
>         unsigned int c;
> };
> #pragma pack()
> struct TestStruct t;
> t.a = 0;      //step 1
> t.b = 1;      //step 2
> t.c = 2;      //step 3
>
> Questing is :  Are these 3 steps having the same perfomance time?

The C language standard says nothing about the relative performance
of various operations, so there is no general answer to your
question.  The language specifies the behavior of programs, not
their performance.

You can answer it for your own system by measuring the performance.

Suppose you find out that one operation is faster than another on
your system; what would you do with that information?  If you need
to assign a value to t.c, assigning a value to t.a might be faster,
but that doesn't do yhou much good if it's not the right thing to do.

(Note that "#pragma pack" is non-standard and potentially unsafe;
see <http://stackoverflow.com/q/8568432/827263>.  For your particular
struct definition, it's unlikely to have any effect.)

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
    Will write code for food.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"
-- 
comp.lang.c.moderated - moderation address: clcm@plethora.net -- you must
have an appropriate newsgroups line in your header for your mail to be seen,
or the newsgroup name in square brackets in the subject line.  Sorry.

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Thread

which one is faster? echo ma <fatmck@gmail.com> - 2012-04-04 18:05 -0500
  Re: which one is faster? James Kuyper <jameskuyper@verizon.net> - 2012-04-23 08:31 -0500
  Re: which one is faster? "Joel C. Salomon" <joelcsalomon@gmail.com> - 2012-04-23 08:33 -0500
  Re: which one is faster? David Brown <david@westcontrol.removethisbit.com> - 2012-04-23 08:33 -0500
  Re: which one is faster? Thomas Richter <thor@math.tu-berlin.de> - 2012-04-23 08:31 -0500
    Re: which one is faster? Keith Thompson <kst-u@mib.org> - 2012-04-30 21:57 -0500
  Re: which one is faster? Barry Schwarz <schwarzb@dqel.com> - 2012-04-23 08:32 -0500
  Re: which one is faster? Keith Thompson <kst-u@mib.org> - 2012-04-23 08:32 -0500
    Re: which one is faster? George Neuner <gneuner2@comcast.net> - 2012-04-30 21:58 -0500

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