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A null pointer has a value reserved for indicating that the pointer does not refer to a valid object. Null pointers are routinely used 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 and to the Nothing value in an option type.
Java references do not allow direct access to memory addresses or allow memory addresses to be manipulated with pointer arithmetic. In C++ one can construct pointers to pointers, pointers to ints and doubles, and pointers to arbitrary memory locations. Java references only access objects, never primitives, other references, or arbitrary memory ...
Code blocks or methods that use the pointers must be marked with the unsafe keyword to be able to use pointers, and the compiler requires the /unsafe switch to allow compiling such code. Assemblies that are compiled using the /unsafe switch are marked as such and may only execute if explicitly trusted. This allows using pointers and pointer ...
Many languages have explicit pointers or references. Reference types differ from these in that the entities they refer to are always accessed via references; for example, whereas in C++ it's possible to have either a std:: string and a std:: string *, where the former is a mutable string and the latter is an explicit pointer to a mutable string (unless it's a null pointer), in Java it is only ...
Java, C#, Ada, and Pascal are sometimes said to be more strongly typed than C, because C supports more kinds of implicit conversions, and allows pointer values to be explicitly cast while Java and Pascal do not. Java may be considered more strongly typed than Pascal as methods of evading the static type system in Java are controlled by the Java ...
C-style pointer use can hinder optimizing in languages that support pointers, The use of escape analysis methods is limited in C++, for example, because a C++ compiler does not always know if an object will be modified in a given block of code due to pointers, [note 1] Java can access derived instance methods faster than C++ can access derived ...
When an object is created, a pointer to this table, called the virtual table pointer, vpointer or VPTR, is added as a hidden member of this object. As such, the compiler must also generate "hidden" code in the constructors of each class to initialize a new object's virtual table pointer to the address of its class's virtual method table.
Use after free – dereferencing a dangling pointer storing the address of an object that has been deleted. Double free – repeated calls to free may prematurely free a new object at the same address. If the exact address has not been reused, other corruption may occur, especially in allocators that use free lists.