C++11 std::function Usage (c + + frequently asked question 17)

c++11 std::function Usage

Directly on the code:

Example 1:std::function feels like a function pointer that has wood

 #include <iostream> #include <functional> #include <map>using namespace std;//normal function int Add (int i, int j) {return i + j;} lambda expression Auto mod = [] (int i, int j) {return I% J;};//function object class struct Divide{int operator () (int denominator, int divisor) {return denominator/divisor;}}; void Main () {//More flexible Mapmap<char, function<int (int, int) >> binops;binops[' + ') = add;binops['-'] = minus< Int> (); binops[' * '] = [] (int i, int j) {return i * j;}; binops['/'] = divide (); binops['% '] = mod;cout << binops[' + '] (5) << endl;cout << binops['-'] (10, 5) & lt;< endl;cout << binops[' * ' [5] << endl;cout << binops['/'] (5) << endl;cout << b inops['% '] (5) << Endl;system ("pause");} 

The above code also briefly describes the "lambda expression","lambda expressions" (lambda expression) is an anonymous function , lambda expression based on the mathematical lambda calculus named, The lambda abstraction (lambda abstraction), which corresponds directly to it, is an anonymous function, that is, a function without a function name. A lambda expression can represent closures (notice differs from the traditional mathematical sense).

c++11 std::bind Usage

Example 2:

The use of std::bind ... Std::bind is more like a wrapper over an existing function (decoration)

#include <iostream> #include <functional> #include <typeinfo> #include <string>using namespace Std;int add1 (int i, int j, int k) {return i + j + k;}        Class Person {Public:person (const char* name): M_strname (name) {} void SayHello (const char* name) Const {    Std::cout << m_strname<< "Say:hello" << name << Std::endl;    } int operator () (int i, int j, int k) const {return i + j + k;    } static string GetClassName () {return string ("person"); } private:string m_strname;};/     * * */int main (void) {//bind global function Auto ADD2 = Std::bind (ADD1, std::p laceholders::_1, std::p laceholders::_2, 10);    function add2 = bind add1 function, parameter 1 is unchanged, parameter 2 is unchanged, parameter 3 is fixed to 10.    Std::cout << typeid (ADD2). Name () << Std::endl;     Std::cout << "Add2" = "<< add2 (1, 2) << Std::endl;        Std::cout << "\ n---------------------------" << Std::endl; The BIND member function is the person man ("Std::fuNction ");    Auto SayHello = Std::bind (&person::sayhello, man/* caller */, std::p laceholders::_1/* parameter 1*/);        SayHello ("Peter");    Auto Sayhellotopeter = Std::bind (&person::sayhello, man/* caller */, "Peter"/* fixed parameter 1*/);        Sayhellotopeter ();    Bind static member function Auto Getclassname= std::bind (&person::getclassname);        Std::cout << getclassname () << Std::endl;        Std::cout << "\ n---------------------------" << Std::endl; Bind operator function Auto add100 = Std::bind (&person::operator (), MAN, std::p laceholders::_1, std::p laceholders::_2, 10    0);        Std::cout << "add100 (1, 2) =" << add100 (1, 2) << Std::endl;    Note: You cannot use Std::bind () to bind an overloaded function system ("pause"); return 0;}

C++11 std::function Usage (c + + frequently asked question 17)