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In computer programming, a callback is a function that is stored as data (a reference) and designed to be called by another function – often back to the original abstraction layer. A function that accepts a callback parameter may be designed to call back before returning to its caller which is known as synchronous or blocking.
Calling f with a regular function argument first applies this function to the value 2, then returns 3. However, when f is passed to call/cc (as in the last line of the example), applying the parameter (the continuation) to 2 forces execution of the program to jump to the point where call/cc was called, and causes call/cc to return the value 2.
Some C libraries support callbacks. This is sometimes implemented by providing two values when registering the callback with the library: a function pointer and a separate void* pointer to arbitrary data of the user's choice. When the library executes the callback function, it passes along the data pointer.
Specifically, C allows a void* pointer to be assigned to any pointer type without a cast, while C++ does not; this idiom appears often in C code using malloc memory allocation, [9] or in the passing of context pointers to the POSIX pthreads API, and other frameworks involving callbacks. For example, the following is valid in C but not C++:
Callback (comedy), a joke which refers to one previously told; Callback (computer programming), callable (i.e. function) that is passed as data and expected to be called by another callable. Callback (telecommunications), the telecommunications event that occurs when the originator of a call is immediately called back in a second call as a response
The advantages of using web pages or domains as C&C is that a large botnet can be effectively controlled and maintained with very simple code that can be readily updated. Disadvantages of using this method are that it uses a considerable amount of bandwidth at large scale, and domains can be quickly seized by government agencies with little effort.
Function pointers allow different code to be executed at runtime. They can also be passed to a function to enable callbacks. Function pointers are supported by third-generation programming languages (such as PL/I, COBOL, Fortran, [1] dBASE dBL [clarification needed], and C) and object-oriented programming languages (such as C++, C#, and D). [2]
The C-family programming languages share significant features of the C programming language.Many of these 70 languages were developmentally influenced by C due to its success and ubiquity.