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Vtable
In computer programming, a virtual method table (VMT), virtual function table, virtual call table, dispatch table, vtable, or vftable is a mechanism used in a programming language to support dynamic dispatch (or run-time method binding). Whenever a class defines a virtual function (or method), most compilers add a hidden member variable to the class that points to an array of pointers to (virtual) functions called the virtual method table. These pointers are used at runtime to invoke the appropriate function implementations, because at compile time it may not yet be known if the base function is to be called or a derived one implemented by a class that inherits from the base class. There are many different ways to implement such dynamic dispatch, but use of virtual method tables is especially common among C++ and related languages (such as D and C#). Languages that separate the programmatic interface of objects from the implementation, like Visual Basic and Delphi, also te ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dynamic Dispatch
In computer science, dynamic dispatch is the process of selecting which implementation of a polymorphic operation (method or function) to call at run time. It is commonly employed in, and considered a prime characteristic of, object-oriented programming (OOP) languages and systems. Object-oriented systems model a problem as a set of interacting objects that enact operations referred to by name. Polymorphism is the phenomenon wherein somewhat interchangeable objects each expose an operation of the same name but possibly differing in behavior. As an example, a object and a object both have a method that can be used to write a personnel record to storage. Their implementations differ. A program holds a reference to an object which may be either a object or a object. Which it is may have been determined by a run-time setting, and at this stage, the program may not know or care which. When the program calls on the object, something needs to choose which behavior gets enacted. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dispatch Table
In computer science, a dispatch table is a table of pointers or memory addresses to functions or methods. Use of such a table is a common technique when implementing late binding in object-oriented programming. Perl implementation The following shows one way to implement a dispatch table in Perl, using a hash to store references to code (also known as function pointers). # Define the table using one anonymous code-ref and one named code-ref my %dispatch = ( "-h" => sub , "-g" => \&say_goodbye ); sub say_goodbye # Fetch the code ref from the table, and invoke it my $sub = $dispatch; print $sub ? $sub->() : "unknown argument\n"; Running this Perl program as perl greet -h will produce "hello", and running it as perl greet -g will produce "goodbye". JavaScript implementation Following is a demo of implementing dispatch table in JavaScript: var thingsWeCanDo = ; var doSomething = function(doWhat) Virtual method tables In object-oriented programming langua ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
D (programming Language)
D, also known as dlang, is a multi-paradigm system programming language created by Walter Bright at Digital Mars and released in 2001. Andrei Alexandrescu joined the design and development effort in 2007. Though it originated as a re-engineering of C++, D is a profoundly different language —features of D can be considered streamlined and expanded-upon ideas from C++, however D also draws inspiration from other high-level programming languages, notably Java, Python, Ruby, C#, and Eiffel. D combines the performance and safety of compiled languages with the expressive power of modern dynamic and functional programming languages. Idiomatic D code is commonly as fast as equivalent C++ code, while also being shorter. The language as a whole is not memory-safe but includes optional attributes designed to guarantee memory safety of either subsets of or the whole program. Type inference, automatic memory management and syntactic sugar for common types allow faster development ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Virtual Function Pointer
In computer programming, a virtual method table (VMT), virtual function table, virtual call table, dispatch table, vtable, or vftable is a mechanism used in a programming language to support dynamic dispatch (or run-time method binding). Whenever a class defines a virtual function (or method), most compilers add a hidden member variable to the class that points to an array of pointers to (virtual) functions called the virtual method table. These pointers are used at runtime to invoke the appropriate function implementations, because at compile time it may not yet be known if the base function is to be called or a derived one implemented by a class that inherits from the base class. There are many different ways to implement such dynamic dispatch, but use of virtual method tables is especially common among C++ and related languages (such as D and C#). Languages that separate the programmatic interface of objects from the implementation, like Visual Basic and Delphi, also t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Constructor (object-oriented Programming)
In class-based, object-oriented programming, a constructor (abbreviation: ctor) is a special type of subroutine called to create an object. It prepares the new object for use, often accepting arguments that the constructor uses to set required member variables. A constructor resembles an instance method, but it differs from a method in that it has no explicit return type, it is not implicitly inherited and it usually has different rules for scope modifiers. Constructors often have the same name as the declaring class. They have the task of initializing the object's data members and of establishing the invariant of the class, failing if the invariant is invalid. A properly written constructor leaves the resulting object in a ''valid'' state. Immutable objects must be initialized in a constructor. Most languages allow overloading the constructor in that there can be more than one constructor for a class, with differing parameters. Some languages take consideration of some sp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Compile Time
In computer science, compile time (or compile-time) describes the time window during which a computer program is compiled. The term is used as an adjective to describe concepts related to the context of program compilation, as opposed to concepts related to the context of program execution ( runtime). For example, ''compile-time requirements'' are programming language requirements that must be met by source code before compilation and ''compile-time properties'' are properties of the program that can be reasoned about during compilation. The actual length of time it takes to compile a program is usually referred to as ''compilation time''. Compile time/Early binding vs Run time The determination of execution model have been set during the compile time stage. Run time- the method of execution and allocation - have been set during the run time and are based on the run time dynamicity. Overview Most compilers have at least the following compiler phases (which therefore occur at c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Run Time (program Lifecycle Phase)
In computer science, runtime, run time, or execution time is the final phase of a computer programs life cycle, in which the code is being executed on the computer's central processing unit (CPU) as machine code. In other words, "runtime" is the running phase of a program. A runtime error is detected after or during the execution (running state) of a program, whereas a compile-time error is detected by the compiler before the program is ever executed. Type checking, register allocation, code generation, and code optimization are typically done at compile time, but may be done at runtime depending on the particular language and compiler. Many other runtime errors exist and are handled differently by different programming languages, such as division by zero errors, domain errors, array subscript out of bounds errors, arithmetic underflow errors, several types of underflow and overflow errors, and many other runtime errors generally considered as software bugs which may or may ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Memory Address
In computing, a memory address is a reference to a specific memory location used at various levels by software and hardware. Memory addresses are fixed-length sequences of digits conventionally displayed and manipulated as unsigned integers. Such numerical semantic bases itself upon features of CPU (such as the instruction pointer and incremental address registers), as well upon use of the memory like an array endorsed by various programming languages. Types Physical addresses A digital computer's main memory consists of many memory locations. Each memory location has a physical address which is a code. The CPU (or other device) can use the code to access the corresponding memory location. Generally only system software, i.e. the BIOS, operating systems, and some specialized utility programs (e.g., memory testers), address physical memory using machine code operands or processor registers, instructing the CPU to direct a hardware device, called the memory controller, to use the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computer Programming
Computer programming is the process of performing a particular computation (or more generally, accomplishing a specific computing result), usually by designing and building an executable computer program. Programming involves tasks such as analysis, generating algorithms, profiling algorithms' accuracy and resource consumption, and the implementation of algorithms (usually in a chosen programming language, commonly referred to as coding). The source code of a program is written in one or more languages that are intelligible to programmers, rather than machine code, which is directly executed by the central processing unit. The purpose of programming is to find a sequence of instructions that will automate the performance of a task (which can be as complex as an operating system) on a computer, often for solving a given problem. Proficient programming thus usually requires expertise in several different subjects, including knowledge of the application domain, specialized algori ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
C++ Syntax
C, or c, is the third letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''cee'' (pronounced ), plural ''cees''. History "C" comes from the same letter as "G". The Semites named it gimel. The sign is possibly adapted from an Egyptian hieroglyph for a staff sling, which may have been the meaning of the name ''gimel''. Another possibility is that it depicted a camel, the Semitic name for which was ''gamal''. Barry B. Powell, a specialist in the history of writing, states "It is hard to imagine how gimel = "camel" can be derived from the picture of a camel (it may show his hump, or his head and neck!)". In the Etruscan language, plosive consonants had no contrastive voicing, so the Greek ' Γ' (Gamma) was adopted into the Etruscan alphabet to represent . Already in the Western Greek alphabet, Gamma first took a '' form in Early Etruscan, then '' in Classical Et ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Subclass (computer Science)
In object-oriented programming, inheritance is the mechanism of basing an object or class upon another object ( prototype-based inheritance) or class ( class-based inheritance), retaining similar implementation. Also defined as deriving new classes ( sub classes) from existing ones such as super class or base class and then forming them into a hierarchy of classes. In most class-based object-oriented languages, an object created through inheritance, a "child object", acquires all the properties and behaviors of the "parent object" , with the exception of: constructors, destructor, overloaded operators and friend functions of the base class. Inheritance allows programmers to create classes that are built upon existing classes, to specify a new implementation while maintaining the same behaviors ( realizing an interface), to reuse code and to independently extend original software via public classes and interfaces. The relationships of objects or classes through inheritance give ris ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Default Constructor
In computer programming languages, the term default constructor can refer to a constructor that is automatically generated by the compiler in the absence of any programmer-defined constructors (e.g. in Java), and is usually a nullary constructor. In other languages (e.g. in C++) it is a constructor that can be called without having to provide any arguments, irrespective of whether the constructor is auto-generated or user-defined. Note that a constructor with formal parameters can still be called without arguments if default arguments were provided in the constructor's definition. C++ In C++, the standard describes the default constructor for a class as a constructor that can be called with no arguments (this includes a constructor whose parameters all have default arguments). For example: class MyClass ; MyClass::MyClass() : x(100) // constructor defined int main() When allocating memory dynamically, the constructor may be called by adding parenthesis after the class na ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
