Amol Ashok Khot

• Feb 2nd, 2007

 

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.