RE: [Dev-C++] arrays in structures

[Ioannis V. <iv...@em...>]

> -----Original Message-----
> From: dev...@li... 
> [mailto:dev...@li...] On Behalf 
> Of OROSZI Balazs
> Sent: Tuesday, August 05, 2003 12:10 AM
> To: dev...@li...
> Subject: Re: [Dev-C++] arrays in structures
> 
> > 
> > M$ says Yes.
> > 
> > From MSDN:
> > 
> > -- cut here --
> > int prop[3][4][6];
> > ...
> > i = prop[2][1][3];


So what?


> So actually, the whole stuff is stored linearly, and the 
> compiler deals 
> with multiplication, to get the final address in memory, 
> relative to prop.
> 
> And another question arose in me, reading the above: multiplication. 
> Isn't that slow? I mean, if I use a loop, and I do a lot of indexing, 
> that results in a lot of multiplication, no? Wouldn't it be 
> better then 
> to just incerement the pointer itself. Like, instead of this:
> 
> int i,array[100];
> for(i=0;i<100;++i){
>    DoSomething(array[i]);
> }
> 
> do this:
> 
> int *i,array[100];
> for(i=array;i<array+100;++i){
>    DoSomething(*i);
> }
> 
> Would it be faster?


No, because the compiler undestands indexing as pointer
addition/subtraction.


So your indxing code above is perceived by the compiler as:

 int i,array[100];

 for(i=0;i<100;++i){
    DoSomething(*(array+i));
 }






Ioannis Vranos
 
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