Function/Bind function Adapter

1. Introduction to function/Bind

A function is a type of template that overload the operator () function call operator. Therefore, an object of each function class is a function object.

BIND is a function adapter that can change the number and order of parameters.

2. Related code

 1 #include <iostream> 2 #include <string> 3 #include <vector> 4 #include <functional> 5 using namespace std; 6  7 void foo(const string &s) 8 { 9     cout << s << endl;10 }11 12 13 int main(int argc, const char *argv[])14 {15     void (*pFunc) (const string &) = &foo;16     pFunc("bar");17 18     function<void (const string&)> f = &foo;19     f("bar");20     21 22     return 0;23 }

In this case, both the pfunc () and F () functions are equivalent to the Foo () functions. Calling the pfunc () and F () functions is equivalent to calling the Foo () function.

Next, we try to use the function template. The Code is as follows:

 1 #include <iostream> 2 #include <string> 3 #include <vector> 4 #include <functional> 5 using namespace std; 6  7 void foo(int i, double d) 8 { 9     cout << i << d << endl;10 }11 12 13 int main(int argc, const char *argv[])14 {15     function<void (int, double)> f = &foo;16     f(12, 4.5);17     18 19     return 0;20 }

Function and bind are used in combination. The Code is as follows:

 1 #include <iostream> 2 #include <string> 3 #include <vector> 4 #include <functional> 5 using namespace std; 6  7 class Foo 8 { 9     public:10         void foo(int i) { cout << i << endl; }        11 12         static void bar(double d) { cout << d << endl; }13 14 };15 16 int main(int argc, const char *argv[])17 {18     //mem_fun void (*)(Foo *, int)19     Foo f;20     (mem_fun(&Foo::foo))(&f, 123); 21 22     function<void (int)> pf = bind(&Foo::foo, 23                                    &f, 24                                    std::placeholders::_1);25     pf(345);26 27     function<void (Foo*, int)> pf2 = bind(&Foo::foo,28                                           std::placeholders::_1,29                                           std::placeholders::_2);30 31     pf2(&f, 456);32 33     function<void (int, Foo*)> pf3 = bind(&Foo::foo,34                     std::placeholders::_2,35                     std::placeholders::_1);36 37     pf3(567, &f);38 39 40 41     return 0;42 }

From the code above, we can see that bind () can adapt to the location and number of parameters.

Let's continue to look at several codes for better understanding.

 1 #include <iostream> 2 #include <string> 3 #include <vector> 4 #include <functional> 5 using namespace std; 6 using namespace std::placeholders; 7  8 void test(int i, double d, const string &s)//int ,double, const string & 的位置分别为1，2,3 9 {10     cout << "i = " << i << " d = " << d << " s = " << s << endl;11 }12 int main(int argc, const char *argv[])13 {14     function<void (int, double, const string&)> f1 = &test;15     f1(12, 3.14, "foo");16 17     //1.void (*)(int, double)18     function<void (int, double)> f2 = //bind()的第一个参数永远为指向函数的指针或地址，int对应_1, double对应_2,缺少一个参数对应_3,因此我们在第三个参数位置直接实参19             std::bind(&test,20                       _1,21                       _2,22                       "foo");23 24     //2.void (*)(double, int, const string &)25     function<void (double, int, const string &)> f3 = 26         std::bind(&test,    //第一个参数为函数地址即&test, 
27                   _2,       //double对应test()函数第二个参数，所以bind的第二个参数位置_228                   _1,29                   _3);30 31     //3.void (*)(const string &, int)32     function<void (const string &, int)> f4 = 33         std::bind(&test,34                   _2,35                   3.4,   //两个参数缺少一个double参数，double参数在test()中为第二个参数，所以在&test以后的第二个参数位置，写个double实参36                   _1);37 38 39     //4. void (*) (const string &, int, double)40     function<void (const string&, int, double)> f541         = std::bind(&test,42                     _2,43                     _3,44                     _1);45     46     //5. void (*)(int)47     function<void (int)> f6 = 48         bind(&test,49              _1,50              3.4,51              "bar");52 53     //6 void(*)(const string &)54     function<void (const string &)> f7 =55         bind(&test,56              12,57              4.5,58              _1);59 60     //7. void (*)()61     function<void()> f8 = 62         bind(&test,63              12,64              4.5,65              "bar");66 }

 

Function/Bind function Adapter