Search results
Results from the WOW.Com Content Network
Dereferencing a null pointer is undefined behavior in C, [7] and a conforming implementation is allowed to assume that any pointer that is dereferenced is not null. In practice, dereferencing a null pointer may result in an attempted read or write from memory that is not mapped, triggering a segmentation fault or memory access violation.
Dereferencing a null pointer in C produces undefined behavior, [7] which could be catastrophic. However, most implementations [citation needed] simply halt execution of the program in question, usually with a segmentation fault. However, initializing pointers unnecessarily could hinder program analysis, thereby hiding bugs.
Dereferencing any of these variables could cause a segmentation fault: dereferencing the null pointer generally will cause a segfault, while reading from the wild pointer may instead result in random data but no segfault, and reading from the dangling pointer may result in valid data for a while, and then random data as it is overwritten.
Another frequent source of dangling pointers is a jumbled combination of malloc() and free() library calls: a pointer becomes dangling when the block of memory it points to is freed. As with the previous example one way to avoid this is to make sure to reset the pointer to null after freeing its reference—as demonstrated below.
Null pointer dereference – A null pointer dereference will often cause an exception or program termination in most environments, but can cause corruption in operating system kernels or systems without memory protection or when use of the null pointer involves a large or negative offset.
Smart pointers are opaque data structures that act like pointers but can only be accessed through particular methods. A handle is an abstract reference, and may be represented in various ways. A common example are file handles (the FILE data structure in the C standard I/O library ), used to abstract file content.
The null object pattern solves this problem by providing a special NullAnimal class which can be instantiated bound to an Animal pointer or reference. The special null class must be created for each class hierarchy that is to have a null object, since a NullAnimal is of no use when what is needed is a null object with regard to some Widget base ...
In C the use of any automatic variable before it has been initialized yields undefined behavior, as does integer division by zero, signed integer overflow, indexing an array outside of its defined bounds (see buffer overflow), or null pointer dereferencing. In general, any instance of undefined behavior leaves the abstract execution machine in ...