What exactly does string assignment do?

[Artlav]

I've been having weird problems with strings and threads.

Given a and b, both of which are "string" type (ansistring, to be precise), what does a:=b; actually do?
Does it allocate the space for a and copy b's content, or does it create a reference from a to b? Or something else?

See an example below.
The procedure is getting called from various threads, and the strings keep disappearing and losing the last character in them.

Both case A and case B give problems, but they differ a bit.

Code: Pascal  [Select][+][-]

1. type dstkrec=record
2.  c:boolean;
3.  n,f:string;
4. end;  
5.  
6. var dstack:array[0..DSTKS-1]of dstkrec;  
7.  
8. procedure add(const fn,dir:string);
9. var i,c:integer;
10. begin    
11.  mutex_lock(ar_mx);
12.   c:=-1;
13.   for i:=0 to DSTKS-1 do if not dstack[i].c then begin c:=i; break; end;
14.   if c<>-1 then begin
15.    dstack[c].c:=true;
16.  
17. {$ifdef casea}
18.    //Case A:
19.    dstack[c].f:=fn;
20.    dstack[c].n:=dir;
21. {$else}
22.    //Case B:
23.    setlength(dstack[c].f,length(fn));
24.    move(fn[1],dstack[c].f[1],length(fn));
25.    setlength(dstack[c].n,length(dir));
26.    move(dir[1],dstack[c].n[1],length(dir));
27. {$endif}
28.  
29.   end;
30.  mutex_release(ar_mx);
31. end;
32.  

[molly]

Ansistrings are reference counted. More information can be read here.

Assigning one ansistring to another doesn’t involve moving the actual string. A statement    S2:=S1;

results in the reference count of S2 being decreased with 1, The reference count of S1 is increased by 1, and finally S1 (as a pointer) is copied to S2.

[User137]

What's best way to copy it into new string, this?

Code: Pascal  [Select][+][-]

1. S2:=S1+'';

[howardpc]

Code: Pascal  [Select][+][-]

1. s2:=s1;
2. UniqueString(s2);