A function object, or functor, is any type that implements operator(). This operator is referred to as the call operator or sometimes the application operator. The C++ Standard Library uses function objects primarily as sorting criteria for containers and in algorithms.
Function objects provide two main advantages over a straight function call. The first is that a function object can contain state. The second is that a function object is a type and therefore can be used as a template parameter.
Creating a Function Object
To create a function object, create a type and implement operator(), such as:
class Functor{public: int operator()(int a, int b) { return a < b; }};int main(){ Functor f; int a = 5; int b = 7; int ans = f(a, b);}
The last line of the main function shows how you call the function object. This call looks like a call to a function, but it's actually calling operator() of the Functor type. This similarity between calling a function object and a function is how the term function object came about.
Function Objects and Containers
The C++ Standard Library contains several function objects in the <functional> header file. One use of these function objects is as a sorting criterion for containers. For example, the set container is declared as follows:
template <class Key, class Traits=less<Key>, class Allocator=allocator<Key>>class set
The second template argument is the function object less. This function object returns true if the first parameter is less than the second parameter. Since some containers sort their elements, the container needs a way of comparing two elements. The comparison is done by using the function object. You can define your own sorting criteria for containers by creating a function object and specifying it in the template list for the container.
Function Objects and Algorithms
Another use of functional objects is in algorithms. For example, the remove_if algorithm is declared as follows:
template <class ForwardIterator, class Predicate>ForwardIterator remove_if( ForwardIterator first, ForwardIterator last, Predicate pred);
The last argument to remove_if is a function object that returns a boolean value (a predicate). If the result of the function object is true, then the element is removed from the container being accessed by the iterators first and last. You can use any of the function objects declared in the <functional> header for the argument pred or you can create your own.
A function object, or functor, is any type that implements operator(). This operator is referred to as the call operator or sometimes the application operator. The C++ Standard Library uses function objects primarily as sorting criteria for containers and in algorithms.
A function object is any object for which the function call operator is defined. C++ provides many built-in function objects as well as support for creation and manipulation of new function objects.
The C++ Standard Template Library (STL) is a collection of algorithms, data structures, and other components that can be used to simplify the development of C++ programs. The STL provides a range of containers, such as vectors, lists, and maps, as well as algorithms for searching, sorting and manipulating data.
In C++, an object is created from a class. We have already created the class named MyClass , so now we can use this to create objects. To create an object of MyClass , specify the class name, followed by the object name.
Every program must have one function named main , and the following constraints apply: No other function in the program can be called main . main cannot be defined as inline or static . main cannot be called from within a program.
A C++ function consist of two parts: Declaration: the return type, the name of the function, and parameters (if any)Definition: the body of the function (code to be executed)
In-built functions in C++ are those functions that are part of C++ standard libraries. The purpose of inbuilt functions is to provide common and essential functionality that is frequently required in the programming.
In C++, an object is an instance of a class that encapsulates data and functionality pertaining to that data. Suppose a class named MyClass was created, so now it can be used to create objects.
Standard libraries typically include definitions for commonly used algorithms, data structures, and mechanisms for input and output. Depending on the constructs made available by the host language, a standard library may include: Subroutines. Macro definitions.
The Standard C++ library provides an extensible framework and contains components for language support, diagnostics, general utilities, strings, locales, standard template library (containers, iterators, algorithms, and numerics), and input/output.
The Standard C++ Library can be categorized as follows: The Language Support Library. The Diagnostics Library. The General Utilities Library. The Standard String Templates.
A function object, or functor, is any type that implements operator(). This operator is referred to as the call operator or sometimes the application operator. The C++ Standard Library uses function objects primarily as sorting criteria for containers and in algorithms.
A function pointer allows a pointer to a function to be passed as a parameter to another function. Function Objects (Functors) - C++ allows the function call operator() to be overloaded, such that an object instantiated from a class can be "called" like a function.
You can use Object.create() to mimic the behavior of the new operator. function Constructor() {} o = new Constructor(); // Is equivalent to: o = Object.create(Constructor.prototype); Of course, if there is actual initialization code in the Constructor function, the Object.create() method cannot reflect it.
The STL provides a set of common classes for C++, such as containers and associative arrays, that can be used with any built-in type and with any user-defined type that supports some elementary operations (such as copying and assignment).
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