Excellent explication !
Thank you Frits
Le Sat, 14 Feb 2009 17:58:35 +0100, Frits van Bommel
<fvbom...@remwovexcapss.nl> a écrit:
TSalm wrote:
Hello,
In the code below, why the first Stdout throws a Exception when the
second doesn't ?
/* -------- CODE -------- */
import tango.io.Stdout;
struct VoidPtr(T)
{
void* vPtr;
void value(T val)
{
vPtr = &val;
Here you're storing a pointer to a non-ref parameter. This is the bug;
the parameter itself is implicitly deallocated on returning from this
function.
Change to 'ref T val' to fix it.
Essentially, an array is a struct { size_t length; T ptr; }. This means
'val' refers to a copy in the stack frame of this function, not to 'arr'
in main().
}
T value()
{
return *(cast(T*)vPtr);
}
}
void main()
{
VoidPtr!(char[][]) vPtr ;
char[][] arr = [ "hello" , "you" ];
vPtr.value = arr ;
Stdout( vPtr.value ).newline; // <--
[tango.core.Exception.OutOfMemoryException: Memory allocation failed
Here you're calling a new function, overwriting *vPtr with something
else (probably vptr itself), resulting in a huge array when you try to
read it later.
Stdout( *(cast(char[][]*) vPtr.vPtr ) ); // <-- This works good
This reads the (implicitly deallocated) 'val' parameter before it gets
overwritten, hiding the bug. It's still there: just because the code
doesn't crash doesn't mean it's correct.
}
/* ------ END CODE ------ */
Thanks in advance for your help,
TSalm
