OOPS - what is dangling pointer?where it is used ? what are the advantages?

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what is dangling pointer?where it is used ? what are the advantages?

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Last Update: February 02, 2007 Asked by: rajan.c

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Submitted by: Amol Ashok Khot

Dangling pointers and wild pointers in computer programming are pointers that do not point to a valid object of the appropriate type, or to a distinguished null pointer value in languages which support this. Dangling pointers arise when an object is deleted or deallocated, without modifying the value of the pointer, so that the pointer still points to the memory location of the deallocated memory. As the system may reallocate the previously freed memory to another process, if the original program then dereferences the (now) dangling pointer, unpredictable behavior may result, as the memory may now contain completely different data. This is especially the case if the program writes data to memory pointed by a dangling pointer, as silent corruption of unrelated data may result, leading to subtle bugs that can be extremely difficult to find, or cause segmentation faults (*NIX) or general protection faults (Windows). If the overwritten data is bookkeeping data used by the system's memory allocator, the corruption can cause system instabilities. Wild pointers arise when a pointer is used prior to initialization to some known state, which is possible in some programming languages. They show the same eratic behaviour as dangling pointers, though they are less likely to stay undetected.

Above answer was rated as good by the following members:
achintya, rajani_vaddepalli15

February 02, 2007 03:23:39

Amol Ashok Khot

RE: what is dangling pointer?where it is used ? what a...

Dangling pointers and wild pointers in computer programming are pointers that do not point to a valid object of the appropriate type or to a distinguished null pointer value in languages which support this. Dangling pointers arise when an object is deleted or deallocated without modifying the value of the pointer so that the pointer still points to the memory location of the deallocated memory. As the system may reallocate the previously freed memory to another process if the original program then dereferences the (now) dangling pointer unpredictable behavior may result as the memory may now contain completely different data. This is especially the case if the program writes data to memory pointed by a dangling pointer as silent corruption of unrelated data may result leading to subtle bugs that can be extremely difficult to find or cause segmentation faults (*NIX) or general protection faults (Windows). If the overwritten data is bookkeeping data used by the system's memory allocator the corruption can cause system instabilities. Wild pointers arise when a pointer is used prior to initialization to some known state which is possible in some programming languages. They show the same eratic behaviour as dangling pointers though they are less likely to stay undetected.

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