Re: NSData confusion
Re: NSData confusion
- Subject: Re: NSData confusion
- From: "Stephen J. Butler" <email@hidden>
- Date: Fri, 20 Mar 2009 15:00:38 -0500
On Fri, Mar 20, 2009 at 2:28 PM, James Maxwell
<email@hidden> wrote:
> okay, but what about matrices?
>
> I've set them up using:
>
> float **theMatrix = [[self matrixData] mutableBytes];
>
> and this part seems okay - or at least, it compiles... But how do I then
> access the matrix.
> I've been using normal C-style array notation, thus far:
>
> theMatrix[i][j] = 0.6666;
>
> but this gives me an EXC_BAD_ACESS error when I run it.
Because this:
float theMatrix[ XSIZE ][ YSIZE ];
is not equivalent to this:
float **theMatrix = /* something */;
The latter says you have an array of float POINTERS. What you want is simple:
float *theMatrix = /* something */;
And then index it with:
theMatrix[ i*XSIZE + j ] = 0.666;
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