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digitalmars.D.learn - pointer array?

reply "seany" <seany uni-bonn.de> writes:
In Ali's excllent book, somehow one thing has escaped my 
attention, and that it the mentioning of pointer arrays.

Can pointers of any type of pointed variable be inserted in an 
int array? Using to!(int) perhaps? If not directly, then what 
else would achieve the same effect?
Jul 30 2014
next sibling parent Justin Whear <justin economicmodeling.com> writes:
On Wed, 30 Jul 2014 14:33:51 +0000, seany wrote:


 In Ali's excllent book, somehow one thing has escaped my attention, and
 that it the mentioning of pointer arrays.
 
 Can pointers of any type of pointed variable be inserted in an int
 array? Using to!(int) perhaps? If not directly, then what else would
 achieve the same effect?


You can use an array of void*: http://dpaste.dzfl.pl/0d3ee1723192
Jul 30 2014
prev sibling next sibling parent reply Leandro Motta Barros via Digitalmars-d-learn writes:
Justin's  answers seems correct to me, and I don't know anything about your
specific use case, but I cannot resist to add:

Think twice before doing this kind of things. I know that sometimes this is
necessary or handy, but one of the great things about D is that it provides
so many higher-level abstractions that we should feel ashamed to not use
them.

So, yes, an array of void* will work in D, as will many of the classic
lower-level tricks used in, say, C. But when using them, the compiler will
not be able to help you much finding errors and such. As rule I'd say that,
if you can (and we usually can), try using something higher level. (In your
case, perhaps an array of objects of some base class, or implementing a
certain interface? Or some more radical redesign?)

Cheers,

LMB



On Wed, Jul 30, 2014 at 11:33 AM, seany via Digitalmars-d-learn <
digitalmars-d-learn puremagic.com> wrote:


 In Ali's excllent book, somehow one thing has escaped my attention, and
 that it the mentioning of pointer arrays.

 Can pointers of any type of pointed variable be inserted in an int array?
 Using to!(int) perhaps? If not directly, then what else would achieve the
 same effect?
Jul 30 2014
parent reply "seany" <seany uni-bonn.de> writes:
Actually, I am writing a climate simulation software, and I would 
love to use D for parts of it.

However some code is in C, legacy code, and for speed resons. So 
in some cases, I would like to send a bunch of variables , ints, 
dubles and floats to an external C function. The thing is, I do 
not always know the number of variables, so my idea was to make 
an array of pointers (call it stack), and then send the pointer 
to the stack itself to the C function.

Because different stack configuration will call different C 
functions, and the function already knowes what to expect in this 
stack, I thought this was a good construction. If I am to create 
a set of base class, and array of it, and so much, it looks very 
complicated....

Of course, for more complicated objects, e.g., Groups, and other 
algebraic objects, I am using DLua.

Any suggestions.
Jul 30 2014
parent reply Justin Whear <justin economicmodeling.com> writes:
On Wed, 30 Jul 2014 15:44:14 +0000, seany wrote:


 However some code is in C, legacy code, and for speed resons. So in some
 cases, I would like to send a bunch of variables , ints, dubles and
 floats to an external C function. The thing is, I do not always know the
 number of variables, so my idea was to make an array of pointers (call
 it stack), and then send the pointer to the stack itself to the C
 function.


Can you post the signatures of some of the C functions you're trying to 
interface with?
Jul 30 2014
parent reply "seany" <seany uni-bonn.de> writes:
 Can you post the signatures of some of the C functions you're 
 trying to
 interface with?


let us take a simple function :

int add (int a, int b)
Jul 30 2014
parent Leandro Motta Barros via Digitalmars-d-learn writes:
Can't you call it directly?

extern(C)
{
   int add (int a, int b)';
}

// ...

auto ret = add(123, 456);



LMB




On Wed, Jul 30, 2014 at 2:55 PM, seany via Digitalmars-d-learn <
digitalmars-d-learn puremagic.com> wrote:


 Can you post the signatures of some of the C functions you're trying to
 interface with?


 let us take a simple function :

 int add (int a, int b)
Jul 30 2014
prev sibling parent reply Daniel Kozak via Digitalmars-d-learn <digitalmars-d-learn puremagic.com> writes:
V Wed, 30 Jul 2014 14:33:51 +0000
seany via Digitalmars-d-learn <digitalmars-d-learn puremagic.com>
napsáno:


 In Ali's excllent book, somehow one thing has escaped my 
 attention, and that it the mentioning of pointer arrays.
 
 Can pointers of any type of pointed variable be inserted in an 
 int array? Using to!(int) perhaps? If not directly, then what 
 else would achieve the same effect?


It depends on pointer size, for eg, on 64bit system with 64bit pointers
something like this should works:
long[] arr = (cast(long*)pointersArray.ptr)[0 .. pointersArray.length];
or
long[] arr = cast(long[])pointersArray; // but I am not sure if this is
OK
Jul 30 2014
parent "FreeSlave" <freeslave93 gmail.com> writes:
On Wednesday, 30 July 2014 at 20:51:25 UTC, Daniel Kozak via 
Digitalmars-d-learn wrote:

 V Wed, 30 Jul 2014 14:33:51 +0000
 seany via Digitalmars-d-learn 
 <digitalmars-d-learn puremagic.com>
 napsáno:


 In Ali's excllent book, somehow one thing has escaped my 
 attention, and that it the mentioning of pointer arrays.
 
 Can pointers of any type of pointed variable be inserted in an 
 int array? Using to!(int) perhaps? If not directly, then what 
 else would achieve the same effect?


 It depends on pointer size, for eg, on 64bit system with 64bit 
 pointers
 something like this should works:
 long[] arr = (cast(long*)pointersArray.ptr)[0 .. 
 pointersArray.length];
 or
 long[] arr = cast(long[])pointersArray; // but I am not sure if 
 this is
 OK


Don't use long in this case, use size_t and ptrdiff_t. They are 
required to be integer types with size of pointer (size_t is 
unsigned, ptrdiff_t is signed)
Jul 31 2014