On Sun, 2007-09-30 at 18:12 +0200, Michael Blizek wrote: > Hi! > > I'm assuming you're working in userspace, since the memory allocation Which leads to the obvious question: What's the relevance of the question to the Linux kernel? > function in the kernel is kmalloc. > > On Sat, 2007-09-29 at 16:49 -0700, Irfan Ahmed wrote: > > I need four dimensional array like > > double a[256][256][256][256]; > > > > > > but the size is too big to use an array. Why? > That's 32 GB memory! Are you *really* sure you want to do this? It would > require a 64 bit system and "some" ram/swap space if you access the > array. You have to do this on the *heap* not on the stack and have to be > careful not to produce an integer overflow. > > > If I use only pointer like > > double ****a; > > > > to allocate this memory, I have to run 3 loops to allocate > > memory ..which takes lots of time. > > Because of 256^3 = ~17 million system calls... And the result will use even more than 32GB because you need also space for the pointers for the last 3 dimensions. > > I was thinking to use *a[256][256][256] > > Can I use this ...and if yes how I can allocate the memory for > > this...? ---- snip ---- a = malloc(sizeof(double) * 256 * 256 * 256). ---- snip ---- But this is only 3-dimensional and (in terms of RAM usage) equivalent to declaring ---- snip ---- double a[256][256][256]; ---- snip ---- and using it. What are you trying to accomplish? > You can do this, but it would be a 3 dimensional array of pointers, > which is probably not what you want. Why not just allocate a memory and > "cast" the pointer to an array? Just assign/use it, no cast necessary. In fact, casting to quiet the compiler hides probably serious errors and problems. Bernd -- Firmix Software GmbH http://www.firmix.at/ mobil: +43 664 4416156 fax: +43 1 7890849-55 Embedded Linux Development and Services -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
