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In computing, a null pointer or null reference is a value saved for indicating that the pointer or reference does not refer to a valid object. Programs routinely use null pointers to represent conditions such as the end of a list of unknown length or the failure to perform some action; this use of null pointers can be compared to nullable types ...
The language does not provide any explicit pointer manipulation operators. It is still possible for code to attempt to dereference a null reference (null pointer), however, which results in a run-time exception being thrown. The space occupied by unreferenced memory objects is recovered automatically by garbage collection at run-time. [20]
In computer programming, a reference is a value that enables a program to indirectly access a particular datum, such as a variable's value or a record, in the computer's memory or in some other storage device. The reference is said to refer to the datum, and accessing the datum is called dereferencing the reference. A reference is distinct from ...
To expose dangling pointer errors, one common programming technique is to set pointers to the null pointer or to an invalid address once the storage they point to has been released. When the null pointer is dereferenced (in most languages) the program will immediately terminate—there is no potential for data corruption or unpredictable behavior.
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.
In C++, because dereferencing a null pointer is undefined behavior, compiler optimizations may cause other checks to be removed, leading to vulnerabilities elsewhere in the code. [29] [30] Some lists may also include race conditions (concurrent reads/writes to shared memory) as being part of memory safety (e.g., for access control).
In the C++ programming language, a reference is a simple reference datatype that is less powerful but safer than the pointer type inherited from C.The name C++ reference may cause confusion, as in computer science a reference is a general concept datatype, with pointers and C++ references being specific reference datatype implementations.
According to the Java spec, any attempt to dereference the null reference must result in an exception being thrown at run-time, specifically a NullPointerException. (It would not make sense to dereference it otherwise, because, by definition, it points to no object in memory.)