Locks-and-keys (computing)

	Locks-and-keys (computing) Locks-and-keys is a solution to dangling pointers in computer programming language A programming language is a system of notation for writing computer programs. Programming languages are described in terms of their Syntax (programming languages), syntax (form) and semantics (computer science), semantics (meaning), usually def ...s. The locks-and-keys approach represents pointers as ordered pairs (key, address) where the key is an integer value. Heap-dynamic variables are represented as the storage for the variable plus a cell for an integer lock value. When a variable is allocated, a ''lock value'' is created and placed both into the variable's cell and into the pointer's key cell. Every access to the pointer compares these two values, and access is allowed only if the values match. When a variable is deallocated, the key of its pointer is modified to hold a value different from the variable's cell. From then on, any attempt to dereference the pointer can be flagged as an erro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	Dangling Pointer Dangling pointers and wild pointers in computer programming are pointers that do not point to a valid object of the appropriate type. These are special cases of memory safety violations. More generally, dangling references and wild references are references that do not resolve to a valid destination. Dangling pointers arise during object destruction, when an object that is pointed to by a given pointer is deleted or deallocated, without modifying the value of that said pointer, so that the pointer still points to the memory location of the deallocated memory. The system may reallocate the previously freed memory, and if the program then dereferences the (now) dangling pointer, '' unpredictable behavior may result'', as the memory may now contain completely different data. If the program writes to memory referenced by a dangling pointer, a silent corruption of unrelated data may result, leading to subtle bugs that can be extremely difficult to find. If the memory has been real ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	Programming Language A programming language is a system of notation for writing computer programs. Programming languages are described in terms of their Syntax (programming languages), syntax (form) and semantics (computer science), semantics (meaning), usually defined by a formal language. Languages usually provide features such as a type system, Variable (computer science), variables, and mechanisms for Exception handling (programming), error handling. An Programming language implementation, implementation of a programming language is required in order to Execution (computing), execute programs, namely an Interpreter (computing), interpreter or a compiler. An interpreter directly executes the source code, while a compiler produces an executable program. Computer architecture has strongly influenced the design of programming languages, with the most common type (imperative languages—which implement operations in a specified order) developed to perform well on the popular von Neumann architecture. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
	Tombstone (programming) Tombstones are a mechanism to detect dangling pointers and mitigate the problems they can cause in computer programs. Dangling pointers can appear in certain computer programming languages, e.g. C, C++ and assembly languages. A tombstone is a structure that acts as an intermediary between a pointer and its target, often heap-dynamic data in memory. The pointer – sometimes called the handle – points only at tombstones and never to its actual target. When the data is deallocated, the tombstone is set to a null (or, more generally, to a value that is illegal for a pointer in the given runtime environment), indicating that the variable no longer exists. This mechanism prevents the use of invalid pointers, which would otherwise access the memory area that once belonged to the now deallocated variable, although it may already contain other data, in turn leading to corruption of in-memory data. Depending on the operating system, the CPU can automatically detect such an invalid ac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	Pointer (computer Programming) In computer science, a pointer is an object in many programming languages that stores a memory address. This can be that of another value located in computer memory, or in some cases, that of memory-mapped computer hardware. A pointer ''references'' a location in memory, and obtaining the value stored at that location is known as ''dereferencing'' the pointer. As an analogy, a page number in a book's index could be considered a pointer to the corresponding page; dereferencing such a pointer would be done by flipping to the page with the given page number and reading the text found on that page. The actual format and content of a pointer variable is dependent on the underlying computer architecture. Using pointers significantly improves performance for repetitive operations, like traversing iterable data structures (e.g. strings, lookup tables, control tables, linked lists, and tree structures). In particular, it is often much cheaper in time and space to copy and deref ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]