Why is Using "this" After Deleting It So Dangerous in C ?

The Pitfalls of Using "this" After Deleting It

The C FAQ cautions against accessing the "this" pointer after calling "delete this," citing four restrictions, including the prohibition of examining, comparing, printing, or casting it. But why is this seemingly innocuous piece of data so dangerous?

The crux of the matter lies in the undefined behavior that ensues after deleting "this." Deleting "this" effectively deallocates the current object, rendering the "this" pointer invalid. Any subsequent operations involving this pointer become unpredictable.

While it might be tempting to cast "this" to an integer or output its value using printf(), the C standard provides no guarantees of these operations' behavior. The compiler is free to interpret these actions in arbitrary ways, such as accessing uninitialized memory or even corrupting the hard drive.

To circumvent this issue, consider making a copy of the "this" pointer as an integer before deleting it. This allows you to preserve the pointer's value for future use without invoking undefined behavior.

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