digitalmars.D - array copy/ref question

Brian Sturk (33/33) Aug 11 2008 I'm trying to get a handle on the array assignment, slicing operations a...

Lars Ivar Igesund (8/12) Aug 11 2008 It means you are trying to copy from the same memory you are copying to ...

Brian Sturk (4/13) Aug 11 2008 Hi there,

Jesse Phillips (36/55) Aug 11 2008 The problem is at the top of the program, this should give you the same

Jesse Phillips (10/23) Aug 12 2008 I know I created that first one to be smaller, here is what it was

Koroskin Denis (10/33) Aug 12 2008 It can be rewritten as following:
Sclytrack (2/16) Aug 12 2008 copy = test.dup; //Is this what you want?

telengard (5/23) Aug 12 2008 Just found that and it does seem to do what I want. Seems like I have o...
Jesse Phillips (7/24) Aug 13 2008 Yes, I probably should have mentioned this as well. However I did wish t...

Jarrett Billingsley (6/21) Aug 11 2008 Nope, it's memmove you're looking for. memcpy over overlapping memory

Brian Sturk <bsturk comcast.net> writes:

I'm trying to get a handle on the array assignment, slicing operations and am a
little confused.  The last copy gives me an "overlapping array copy".  Both
arrays have a length of 4.  Is it that I cannot copy from one dynamic array to
another (even if the same size)?

If I'm reading the docs correctly the copy syntax is to have the lhs use the
brackets.

Here is my program:

import std.stdio;

///////////////////////////////////

void
main( string[] args )
{
    int[] test = [ 1, 2, 3, 4 ];
    int[] copy;

    copy = test;

    test[1] = 7;

    writefln( "Ref: test[1] %d copy[1] %d", test[1], copy[1] );

    assert( test[1] == 7 );
    assert( copy[1] == 7 );

    copy    = test[];
    test[1] = 9;

    assert( test[1] == 9 );
    assert( copy[1] == 9 );

    writefln( "Alt ref syntax: test[1] %d copy[1] %d", test[1], copy[1] );

    writefln( "%d %d", test.length, copy.length );

    copy[]  = test;     /* Want to copy, get Error: overlapping array copy */
    test[1] = 11;

    assert( test[1] == 11 );
    assert( copy[1] == 9 );

    writefln( "Copy: test[1] %d copy[1] %d", test[1], copy[1] );
}

Output:

 ./test_ref
Ref: test[1] 7 copy[1] 7
Alt ref syntax: test[1] 9 copy[1] 9
4 4
Error: overlapping array copy

Aug 11 2008

Lars Ivar Igesund <larsivar igesund.net> writes:

Brian Sturk wrote:

 I'm trying to get a handle on the array assignment, slicing operations and
 am a little confused.  The last copy gives me an "overlapping array copy".
  Both arrays have a length of 4.  Is it that I cannot copy from one
 dynamic array to another (even if the same size)?

It means you are trying to copy from the same memory you are copying to -
your arrays reference the same memory.

-- 
Lars Ivar Igesund
blog at http://larsivi.net
DSource, #d.tango & #D: larsivi
Dancing the Tango

Aug 11 2008

Brian Sturk <bsturk comcast.net> writes:

Lars Ivar Igesund Wrote:

 Brian Sturk wrote:
 
 I'm trying to get a handle on the array assignment, slicing operations and
 am a little confused.  The last copy gives me an "overlapping array copy".
  Both arrays have a length of 4.  Is it that I cannot copy from one
 dynamic array to another (even if the same size)?

 
 It means you are trying to copy from the same memory you are copying to -
 your arrays reference the same memory.

Hi there,

Thanks for the clarification, sounds like I need to do a memcpy to do a true
copy.

~telengard

Aug 11 2008

Jesse Phillips <jessekphillips gmail.com> writes:

On Mon, 11 Aug 2008 21:20:32 -0400, Brian Sturk wrote:

 Lars Ivar Igesund Wrote:
 
 Brian Sturk wrote:
 
 I'm trying to get a handle on the array assignment, slicing
 operations and am a little confused.  The last copy gives me an
 "overlapping array copy".
  Both arrays have a length of 4.  Is it that I cannot copy from one
 dynamic array to another (even if the same size)?

 
 It means you are trying to copy from the same memory you are copying to
 - your arrays reference the same memory.

 
 Hi there,
 
 Thanks for the clarification, sounds like I need to do a memcpy to do a
 true copy.
 
 ~telengard

The problem is at the top of the program, this should give you the same 
error:

main( string[] args )
{
    int[] test = [ 1, 2, 3, 4 ];
    int[] copy;

    copy = test;

    test[1] = 7;

    writefln( "Ref: test[1] %d copy[1] %d", test[1], copy[1] );

    assert( test[1] == 7 );
    assert( copy[1] == 7 );

    copy    = test[];
    test[1] = 9;

    assert( test[1] == 9 );
    assert( copy[1] == 9 );

    writefln( "Alt ref syntax: test[1] %d copy[1] %d", test[1], copy[1] );

    writefln( "%d %d", test.length, copy.length );

    copy[]  = test;     /* Want to copy, get Error: overlapping array copy
    */ test[1] = 11;

    assert( test[1] == 11 );
    assert( copy[1] == 9 );

    writefln( "Copy: test[1] %d copy[1] %d", test[1], copy[1] );
}

You created copy and told it to point to test, you would need to 
initialize copy to its own memory.

main( string[] args )
{
    int[] test = [ 1, 2, 3, 4 ];
    int[] copy = new int[4];

    copy[]  = test;     
    test[1] = 11;

    assert( test[1] == 11 );
    assert( copy[1] == 2 );

    writefln( "Copy: test[1] %d copy[1] %d", test[1], copy[1] );
}

Aug 11 2008

Jesse Phillips <jessekphillips gmail.com> writes:

On Tue, 12 Aug 2008 02:42:17 +0000, Jesse Phillips wrote:

 main( string[] args )
 {
     int[] test = [ 1, 2, 3, 4 ];
     int[] copy = new int[4];
 
     copy[]  = test;
     test[1] = 11;
 
     assert( test[1] == 11 );
     assert( copy[1] == 2 );
 
     writefln( "Copy: test[1] %d copy[1] %d", test[1], copy[1] );
 }

I know I created that first one to be smaller, here is what it was 
supposed to be.

void main( string[] args )
{
    int[] test = [ 1, 2, 3, 4 ];
    int[] copy;

    copy = test;

    copy[]  = test;
}

Aug 12 2008

"Koroskin Denis" <2korden gmail.com> writes:

On Tue, 12 Aug 2008 18:12:52 +0400, Jesse Phillips  
<jessekphillips gmail.com> wrote:

 On Tue, 12 Aug 2008 02:42:17 +0000, Jesse Phillips wrote:

 main( string[] args )
 {
     int[] test = [ 1, 2, 3, 4 ];
     int[] copy = new int[4];

     copy[]  = test;
     test[1] = 11;

     assert( test[1] == 11 );
     assert( copy[1] == 2 );

     writefln( "Copy: test[1] %d copy[1] %d", test[1], copy[1] );
 }

 I know I created that first one to be smaller, here is what it was
 supposed to be.

 void main( string[] args )
 {
     int[] test = [ 1, 2, 3, 4 ];
     int[] copy;

     copy = test;

     copy[]  = test;
 }

It can be rewritten as following:

void main()
{
     int[] test = [ 1, 2, 3, 4 ];
     test[] = test;
}

Do you see now that arrays overlap?
It is illegal, use custom routines if you suspect that your data overlaps.

Aug 12 2008

Sclytrack <sclytrack pi.be> writes:

== Extrait de l'article de ��Jesse Phillips (jessekphillips gmail.com)��
 On Tue, 12 Aug 2008 02:42:17 +0000, Jesse Phillips wrote:
 main( string[] args )
 {
     int[] test = [ 1, 2, 3, 4 ];
     int[] copy = new int[4];

     copy[]  = test;
     test[1] = 11;

     assert( test[1] == 11 );
     assert( copy[1] == 2 );

     writefln( "Copy: test[1] %d copy[1] %d", test[1], copy[1] );
 }


copy = test.dup;  //Is this what you want?

Aug 12 2008

telengard <bsturk comcast.net> writes:

Sclytrack Wrote:

 == Extrait de l'article de � Jesse Phillips (jessekphillips gmail.com) �
 On Tue, 12 Aug 2008 02:42:17 +0000, Jesse Phillips wrote:
 main( string[] args )
 {
     int[] test = [ 1, 2, 3, 4 ];
     int[] copy = new int[4];

     copy[]  = test;
     test[1] = 11;

     assert( test[1] == 11 );
     assert( copy[1] == 2 );

     writefln( "Copy: test[1] %d copy[1] %d", test[1], copy[1] );
 }


 
 copy = test.dup;  //Is this what you want?
 

Just found that and it does seem to do what I want.  Seems like I have other
issues though from reading the responses.  Much to learn.   :)

I think I'm projecting too much of my python stuff onto D.  I thought I could
just slice an array into a newly declared one as I would in python.

thanks for the info everyone, much appreciated.

~telengard

Aug 12 2008

Jesse Phillips <jessekphillips gmail.com> writes:

On Tue, 12 Aug 2008 14:51:39 +0000, Sclytrack wrote:

 == Extrait de l'article de « Jesse Phillips (jessekphillips gmail.com) »
 On Tue, 12 Aug 2008 02:42:17 +0000, Jesse Phillips wrote:
 main( string[] args )
 {
     int[] test = [ 1, 2, 3, 4 ];
     int[] copy = new int[4];

     copy[]  = test;
     test[1] = 11;

     assert( test[1] == 11 );
     assert( copy[1] == 2 );

     writefln( "Copy: test[1] %d copy[1] %d", test[1], copy[1] );
 }


 
 copy = test.dup;  //Is this what you want?

Yes, I probably should have mentioned this as well. However I did wish to 
give him an idea of what was causing the overlapping. I should also note 
that with the demonstrated method you are able to copy into a slice of an 
array.

copy[1..5] = test[4..8]; or even
test[0..2] = test[3..5]; // As long as they don't overlap :)

Aug 13 2008

"Jarrett Billingsley" <kb3ctd2 yahoo.com> writes:

"Brian Sturk" <bsturk comcast.net> wrote in message 
news:g7qoh0$2vvr$1 digitalmars.com...
 Lars Ivar Igesund Wrote:

 Brian Sturk wrote:

 I'm trying to get a handle on the array assignment, slicing operations 
 and
 am a little confused.  The last copy gives me an "overlapping array 
 copy".
  Both arrays have a length of 4.  Is it that I cannot copy from one
 dynamic array to another (even if the same size)?

 It means you are trying to copy from the same memory you are copying to -
 your arrays reference the same memory.

 Hi there,

 Thanks for the clarification, sounds like I need to do a memcpy to do a 
 true copy.

Nope, it's memmove you're looking for.  memcpy over overlapping memory 
regions has undefined behavior.  Incidentally, for the same reasons 
overlapping slice copies are illegal -- to allow for the use of faster 
hardware copies that disallow overlapping regions.

Aug 11 2008

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digitalmars.D - array copy/ref question