I thought that if I create a struct in a loop, a new struct would be created each time, but if you see below, it's the same object. How can I create a new struct each iteration?

import std.stdio;

struct Test
{}

void main()
{
	for (int i=0;i < 2; i++)
	{
		Test t;
		writefln("Pointer: ", cast(int)&t);
	}
}

Simen Haugen wrote:
> I thought that if I create a struct in a loop, a new struct would be created each time, but if you see below, it's the same object. How can I create a new struct each iteration?
> 
> import std.stdio;
> 
> struct Test
> {}
> 
> void main()
> {
> 	for (int i=0;i < 2; i++)
> 	{
> 		Test t;
> 		writefln("Pointer: ", cast(int)&t);
> 	}
> }

It *is* a new struct each time:
---
urxae@urxae:~/tmp$ cat test.d
import std.stdio;

struct Test
{ int k = 100; }

void main()
{
        for (int i=0;i < 2; i++)
        {
                Test t;
                writefln(t.k);
                t.k = i;
                writefln("Pointer: ", cast(int)&t);
        }
}
urxae@urxae:~/tmp$ dmd -run test.d
100
Pointer: -1077296716
100
Pointer: -1077296716
---

But after each iteration of the loop, the struct used is destroyed, and the most convenient place to put the next one happens to be the same place as the most convenient place to put the last one...

Simen Haugen wrote:
> > I thought that if I create a struct in a loop, a new struct would be created each time, but if you see below, it's the same object. How can I create a new struct each iteration?
> >
> > import std.stdio;
> >
> > struct Test
> > {}
> >
> > void main()
> > {
> > 	for (int i=0;i < 2; i++)
> > 	{
> > 		Test t;
> > 		writefln("Pointer: ", cast(int)&t);
> > 	}
> > }
> >

A struct is just a regular local variable, ie. allocated on the stack.
Each time 'Test t;' is executed, the same space is initialized. So it's
overwritten, but it doesn't move.  Except that empty structs might not get initialized, even though they have a size of one byte.  You can allocate on the heap with 'new' if you want each instance to be unique.

Try this:

Test* t = new Test;
writefln("Pointer: ", cast(int)t);

Frits van Bommel Wrote:
> It *is* a new struct each time:
(...)
> But after each iteration of the loop, the struct used is destroyed, and the most convenient place to put the next one happens to be the same place as the most convenient place to put the last one...

I see. I stored the pointer in another array, so I thought it wouldn't go out of scope. I guess this only works for object allocated on the heap...?

Simen Haugen wrote:
> 
> I see. I stored the pointer in another array, so I thought it wouldn't
> go out of scope. I guess this only works for object allocated on the
> heap...?

exactly, struct are stored like ints, on the stack and accessing them is invalid after the end of that scope.