ostrstream question

[becte]

I encountered the following code similar to this
// some header files
static char* func(int i)
{
ostrstream out;

if (i==1) out << "ABCDE";
else if (i==2) out << "123";
else cout << "";

return out.str();
}

int main ()
{
static char *p1 = NULL, *p2 = NULL;
p1 = func(1);
p2 = func(2);
printf ("String1 = %s, String2 = %s\n", p1, p2);
return 0;
}
The desired out put is "String1 = ABCDE, String2 = 123".
New if I used an character array, char out[10], and returning &out[0]
instead of ostrstream this would definitly be illegal.
But this looks illegal too, I suppose ostrstream has some destructor
that deletes any allocated memory. What is confusing is that this
happens to work when i try it. Is this legal after all?

[Victor Bazarov]

Re: ostrstream question

becte wrote:[color=blue]
> I encountered the following code similar to this
> // some header files
> static char* func(int i)
> {
> ostrstream out;
>
> if (i==1) out << "ABCDE";
> else if (i==2) out << "123";
> else cout << "";
>
> return out.str();[/color]

You're returning a property of an object about to be destroyed.
[color=blue]
> }
>
> int main ()
> {
> static char *p1 = NULL, *p2 = NULL;
> p1 = func(1);[/color]

p1 here is invalid because it contains a pointer value to a buffer of
a stream that is no more.
[color=blue]
> p2 = func(2);[/color]

Same problem here. p2 is invalid.
[color=blue]
> printf ("String1 = %s, String2 = %s\n", p1, p2);
> return 0;
> }
> The desired out put is "String1 = ABCDE, String2 = 123".
> New if I used an character array, char out[10], and returning &out[0]
> instead of ostrstream this would definitly be illegal.[/color]

Right.
[color=blue]
> But this looks illegal too, I suppose ostrstream has some destructor
> that deletes any allocated memory. What is confusing is that this
> happens to work when i try it. Is this legal after all?[/color]

No.

V