deallocating memory twice

[binaya]

Hi all,

what actually goes wrong when I deallocated the memory twice ..?
say I have

int *p;
p=new(int);

now i run the command;

delete p;
delete p;

what actually happens behind the scene ?

 

[tom_usenet]

Hi all,

what actually goes wrong when I deallocated the memory twice ..?
say I have

int *p;
p=new(int);

now i run the command;

delete p;

Deletes the memory that p points to. p now points to this deallocated
memory region (and strictly speaking has an indeterminate value).

delete p;

This runs the deallocation algorithm on the same bit of memory, which
could do pretty much anything depending on the memory allocation
algorithm used. It might overwrite another bit of memory or similar.
Generally the effect of this is known as "heap corruption", and can
lead to crashes in code that runs much later.

what actually happens behind the scene ?

It depends on the memory allocator used by your compiler/library.

Tom

 

[Ron Natalie]

delete p;
delete p;

what actually happens behind the scene ?

Undefined behavior. Depends on your environment. Perhaps it detects
you're freeing memory twice at runtime and issues an exception, perhaps
it just hoses up the allocation structures. Maybe it is a disaster of biblical proportions.
Fire and brimstone coming down from the skies. Rivers and seas boiling!
40 years of darkness, earthquakes, volcanos. The dead rising from the grave!
Human sacrifice, dogs and cats, living together... mass hysteria!