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Message from discussion Getting a pointer to the memory behind a numpy structured dtype
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mark florisson  
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 More options Aug 12 2012, 6:31 am
From: mark florisson <markflorisso...@gmail.com>
Date: Sun, 12 Aug 2012 11:31:02 +0100
Local: Sun, Aug 12 2012 6:31 am
Subject: Re: [cython-users] Getting a pointer to the memory behind a numpy structured dtype
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On 11 August 2012 22:57, Nathaniel Smith <n...@vorpus.org> wrote:

> Hi all,

> I have a problem that's probably pretty simple, but I'm not sure how
> to go about it. I have a numpy array with an arbitrary structured
> dtype:

>   a = np.zeros(10, dtype=["i2,i4"])

> Each entry in this array is a packed struct -- a 2-byte integer
> followed by a 4-byte integer. But, I want to be able to handle
> arbitrary dtypes of this form, and don't care about their internal
> structure. I want to be able to take an index

>   a[i]

> and get a void* or char* to the 6 bytes representing that entry in the
> array, suitable for passing to memcmp() and such. Regardless of the
> actual dtype of the array.

> How do I efficiently, in Cython, convert an array of arbitrary dtype +
> an index into a void*?

> Cheers,
> -n

If the size of the dtype is variable it isn't really possible. If it's
static you can probably declare a (packed) struct of char[n] and use
the numpy view or astype method.

 
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