Re: Dangling pointer?

[bobduff@world.std.com (Robert A Duff)]

In article <4l0r36$jte@dewey.csun.edu>, chen <kc44097@csun.edu> wrote:
>
>    What is "dangling pointer",can someone give me a defination and example?
>Please e-mail me kc44097@huey.csun.edu

A dangling pointer is a pointer that points to something that no longer
exists, or is invalid in some way.  For example:

    X: Some_Pointer := new Whatever;
    Y: Some_Pointer := X;
    ...
    Free(Y);
    ... -- Now, X is a dangling pointer, and you better not say X.all.

You can also create dangling pointers by using the 'Unchecked_Access
attribute to create a pointer to a local variable, and save that pointer
in a global.  When the procedure is left, the global contains a dangling
pointer.

In general, in Ada, dereferencing dangling errors is not detected -- you
won't usually get a sensible error message, but your program may go
haywire.

According to the RM, it's not a bug to create dangling pointers.  It's a
bug to deference them.

- Bob