Re: [eigen] odd behaviour of operator[]

[Mark Borgerding <mark@xxxxxxxxxxxxxx>]

Here's what I think is happening (anyone correct me if I'm wrong):

The odd behavior is not due to the square braces.  It is the standard 
behavior of the comma operator. 
"states[a,0]" evaluates the expression list a,0 and then uses the last 
expression "0" as the evaluation result.
So "states[a,0]" is equivalent to "states[0]".

The square bracket operator cannot take multiple arguments, which is why 
Eigen uses parens instead.




Andre Krause wrote:
> dear list,
>
> today i coded a little code fragment and typed square braces instead of round ones:
>
> MatrixXf states(N, 3);
>
> for(int a=0;a < N;a++)
> {
> 	states[a, 0] = sin(0.1*a);
> 	states[a, 1] = sin(0.2*a);
> 	states[a, 2] = sin(0.3*a);
> }
>
> oddly enough, this code compiles fine and executes without asserts, but assigns
> strange values to the array. so this obviously does not work but the error is
> not catched by eigen2.0.2.
>
>
>
> of course, this way work
>
> MatrixXf states(N, 3);
>
> for(int a=0;a < N;a++)
> {
> 	states(a, 0) = sin(0.1*a);
> 	states(a, 1) = sin(0.2*a);
> 	states(a, 2) = sin(0.3*a);
> }
>
>
> might there be a way to detect the pitfall of accessing
> 2d matrixes with square braces ? at least, one could disable operator[]
> completely...
>
>