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- To: eigen@xxxxxxxxxxxxxxxxxxx
- Subject: Re: [eigen] odd behaviour of operator[]
- From: Tim Hutt <tdhutt@xxxxxxxxx>
- Date: Thu, 18 Jun 2009 18:54:25 +0100
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2009/6/18 Andre Krause <post@xxxxxxxxxxxxxxxx>:
> 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.
GCC gives a warning about the ',' operator having no effect. Due to
operator precedence and stuff, the comma is evaluated and then the
result of that comma is passed to the [] operator.
It is the equivalent of writing: states[(a, 0)] = sin(0.1*a);
Which is the same as: a; states[0] = sin(0.1*a);
See http://msdn.microsoft.com/en-us/library/zs06xbxh(VS.80).aspx