Hello, everybody

When I tried to program an knight problem, I use a loop to test every case, but only the answer of first case is correct. After print some variable, I suspect it is caused by static array member.

So I wrote a simplest code to test, it looks like following (full code is in the attachment), I found that every instance seems share the same array even another instance changed the elements in array.

class TestArray {
    int [] x = [0,0,0,0,0];
    void doSomething () { // Increase every element in array by 1}
}

void main ()
{
    for (int i = 0; i < 5; i++) {
        TestArray t = new TestArray();
        t.doSomething();
        // Print array.
    }
}

I tried gdc/dmd at Linux/Windows all have same result, so I wondered is this a design rationale for memory space and efficiency?

Currently I use add an constructor and in the constructor do x = x.dup in order to create an whole new dynamic array which only belong to specific instance, is my method correctly?

--
Brian Hsu

Brian Hsu wrote:
> Hello, everybody
> 
> When I tried to program an knight problem, I use a loop to test every
> case, but only the answer of first case is correct. After print some
> variable, I suspect it is caused by static array member.
> 
> So I wrote a simplest code to test, it looks like following (full
> code is in the attachment), I found that every instance seems share
> the same array even another instance changed the elements in array.
> 
> class TestArray { int [] x = [0,0,0,0,0]; void doSomething () { //
> Increase every element in array by 1} }
> 
> void main () { for (int i = 0; i < 5; i++) { TestArray t = new
> TestArray(); t.doSomething(); // Print array. } }
> 
> I tried gdc/dmd at Linux/Windows all have same result, so I wondered
> is this a design rationale for memory space and efficiency?

Not sure.  It appears the array literal:

[0,0,0,0,0,0,0,0,0,0]

creates a single array of int's in memory and the assignment:

int[] x = [0,0,0,0,0,0,0,0,0,0];

causes the array reference 'x' to refer to that signle instance in all class instances.

Whereas what you actually want/expect is for the assignment to create a new array in memory and copy the contents of the literal.

> Currently I use add an constructor and in the constructor do x =
> x.dup in order to create an whole new dynamic array which only belong
> to specific instance, is my method correctly?

It works.

Regan

"Brian Hsu" <brianhsu.hsu@gmail.com> wrote in message news:fdj5bv$pab$1@digitalmars.com...
>
> Currently I use add an constructor and in the constructor do x = x.dup in order to create an whole new dynamic array which only belong to specific instance, is my method correctly?

Yes.  Regan hit the nail on the head in explaining it, and yes, this is the right way to do it.