Re: allocate a 2d array of floats?
Re: allocate a 2d array of floats?
- Subject: Re: allocate a 2d array of floats?
- From: Alastair Houghton <email@hidden>
- Date: Sat, 22 Nov 2003 00:32:05 +0000
On 22 Nov 2003, at 00:18, Jay Rimalrick wrote:
>
Thanks for everyone's advise on the dynamic 2d array i ended up with
>
this
>
code to do the job, however how do I assign values without doing it
>
cell by
>
cell? The last assignment with 'a' does not work in this dynamic
>
state but
>
does work when you define a 2d array statically ... any suggestions?
You can't. You have to assign to individual elements. C doesn't
really support 2D dynamically allocated arrays (you have to code them
yourself, as you've already discovered).
>
a = (float **) malloc (sizeof (float *) * 7);
>
int n;
>
>
for (n = 0; n < 7; ++n)
>
a[n] = (float *) malloc (sizeof (float) * 5);
Do you really need to malloc() the rows separately? If not, then the
example I posted shows you how to do it with two malloc() calls rather
than the eight that your code does. (What's more, the example I posted
will *always* do two malloc()'s, whereas your way you do 1 + H malloc()
calls, where H is the number of rows in your array.)
Another advantage of the code I posted is that memory locality is
potentially much better, because all of the data will be held in a
single block of memory. With the above code, the small malloc()
requests might be spread about in memory, reducing performance.
Kind regards,
Alastair.
[demime 0.98b removed an attachment of type application/pkcs7-signature which had a name of smime.p7s]
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