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digitalmars.D.bugs - [Issue 523] New: I think this is a GC bug

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=523

           Summary: I think this is  a GC bug
           Product: D
           Version: 0.175
          Platform: PC
        OS/Version: Windows
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla digitalmars.com
        ReportedBy: theos list.ru


I think that this is a bug in gc/compiler

char [] foo() {
  char [10] arr = "hello, wor";
  return arr[0..4]; // or return arr;
}

void main() {
  printf(foo());
}

doesn`t work - it prints some rubbish, so, as i guess, arr is collected
when function 'foo' returns. if I use char [] instead of char[10] all works
fine.


-- 
Nov 15 2006
next sibling parent "Jarrett Billingsley" <kb3ctd2 yahoo.com> writes:
<d-bugmail puremagic.com> wrote in message 
news:bug-523-3 http.d.puremagic.com/issues/...

 I think that this is a bug in gc/compiler

 char [] foo() {
  char [10] arr = "hello, wor";
  return arr[0..4]; // or return arr;
 }

 void main() {
  printf(foo());
 }

 doesn`t work - it prints some rubbish, so, as i guess, arr is collected
 when function 'foo' returns. if I use char [] instead of char[10] all 
 works
 fine.

You'll get the same thing in C or C++, because in D, as in those languages, statically-sized arrays are on the stack. When you return the slice of that data, you're hiding from the compiler the fact that you're returning a pointer to a stack variable. You can fix this by using "return arr[0 .. 4].dup;", as that'll copy the data from the stack onto the heap. When you use dynamic arrays, though, they're always allocated on the heap, so it works fine.
Nov 15 2006
prev sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=523


bugzilla digitalmars.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |INVALID




------- Comment #1 from bugzilla digitalmars.com  2006-12-01 02:52 -------
char[10] arr;
allocates arr on the stack. Returning a pointer to the stack will result in
corrupted data.
char[] arr = "string";
will make arr a reference to the static data literal "string", which is in the
static data segment and so remains valid when the function exits.

Not a compiler or gc bug.


-- 
Dec 01 2006