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Signals and slots is a language construct introduced in Qt [1] for communication between objects which makes it easy to implement the observer pattern while avoiding boilerplate code. The concept is that GUI widgets , and other objects, can send signals containing event information which can be received by other objects using special member ...
libsigc++ implements a callback system for use in abstract interfaces and general programming. libsigc++ is one of the earliest implementations of the signals and slots concept implemented using C++ template metaprogramming. It was created as an alternative to the use of a meta compiler such as found in the signals and slots implementation in Qt.
In assembly, C, C++, Pascal, Modula2 and other languages, a callback function is stored internally as a function pointer. Using the same storage allows different languages to directly share callbacks without a design-time or runtime interoperability layer. For example, the Windows API is accessible via multiple languages, compilers and assemblers.
It interprets certain macros from the C++ code as annotations, and uses them to generate added C++ code with meta information about the classes used in the program. This meta information is used by Qt to provide programming features not available natively in C++: signals and slots, introspection and asynchronous function calls. Language bindings
The Meta object system consists of 3 things: QObject class, Q_OBJECT macro and a tool called moc (Meta-Object Compiler).QObject is the base class for all Qt classes, Q_OBJECT macro is used to enable meta-object features in classes and finally moc is a preprocessor that changes Q_OBJECT macro instances to C++ source code to enable meta object system mechanism in the class in which it is used.
The scripting language is based on the ECMAScript standard with a few extensions, such as QObject-style signal and slot connections. [1] The library contains the engine, and a C++ API for evaluating QtScript code and exposing custom QObject-derived C++ classes to QtScript.
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In the C Standard Library, signal processing defines how a program handles various signals while it executes. A signal can report some exceptional behavior within the program (such as division by zero ), or a signal can report some asynchronous event outside the program (such as someone striking an interactive attention key on a keyboard).