C + + class member function pointer class member data pointer

normal function pointer: "Return_type (*ptr_name) (para_types)"

Class member function pointer: "Return_type (class_name::* ptr_name) (para_types)"

Class data member pointer: "type class_name::* ptr_name";

C + +:

1 classDemo2 {3  Public:4Demo ():d ATA ( -)5     {6 7     }8     intdata;9     intShowintAintb)Ten     { One         returnA +b; A     } - }; -  the  -  - intMainintargcChar**argv) - { + Demo A; -demo* b=NewDemo; +     //Complete Declaration and assignment A     intDemo::* int_ptr=&Demo::d ata; at     //No data information after assignment, need object dereference to get data -std::cout<<a.*int_ptr<<Std::endl; -std::cout<<b->*int_ptr<<Std::endl; -  -      -     //class member function pointers in     int(Demo::* ptr) (int,int) =&demo::show; -std::cout<< (A.*PTR) (1,2) <<Std::endl; to  +     return 0; -}

STL algorithms sometimes require a function of a class member, whereas a class member function pointer is not a callable object,functor<> bind MEM_FN is different in its own way, but internally it is implicitly passed the this pointer to fetch data by dereference or call function

A/C + + extension:

1 //The member function pointer uses the2 3 class Screen4 {5  Public:6     enumACTION7     {8 Up_, Down_, Left_, Right_9     };Ten  OneScreen () =default; A  -Screen &Move (ACTION para) -     { the         return( This->*Menu[para]) (); -     } -  - Private: +     usingaction= -Screen &-screen::*)(); +  A  at     StaticAction menu[]; -  -Screen &Up () -     { -Std::cout <<" up"<<Std::endl; -         return* This; in     } -  toScreen &Down () +     { -Std::cout <<" Down"<<Std::endl; the         return* This; *     } $ Panax NotoginsengScreen &Left () -     { theStd::cout <<" Left"<<Std::endl; +         return* This; A     } the  +Screen &Right () -     { $Std::cout <<" Right"<<Std::endl; $         return* This; -     } -  the }; - WuyiScreen::action screen::menu[]{&screen::up, &screen::D Own, &screen::left, &Screen::right}; the  -  Wu intMain () - { About Screen obj; $ obj. Move (SCREEN::UP_); - obj. Move (screen::D own_); - obj. Move (Screen::left_); - obj. Move (screen::right_); A obj. Move (screen::right_); +  the  -     return 0; $ } the  the  the  the#include <iostream> -#include <vector> in#include <functional> the#include <algorithm> the#include <string> About  the //class member function pointers are not callable objects, generic STL algorithms need to wrap class member function pointers as callable objects the //These three packages are internally called by obtaining the object returned by the container, ". *"/"->*"; the //1.std::function< member function type (the first parameter is set to the type of the object itself) > fcn=&std::xxxx::xxx; Difference: The first parameter is the incoming object type, depending on whether the container is a reference or a pointer selection (. */->*) + //2.std::bind (&std::string::empty,std::p laceholders::_1) Differences: You can execute member functions by pointers or objects; - //3.std::mem_fn (&std::string::empty) c++11, Difference: member functions can be executed by pointers and objects the //4. can use LAMDA call;Bayi  the  the classStr - { -  Public: theSTD::stringstr; the  theSTR (ConstSTD::string&str_): Str (STR_) the     { -  the     } the  theSTR (Const Char*str_): Str (STR_)94     { the  the     } the 98     BOOLEmpty ()Constnoexcept About     { -         returnstr.empty ();101     }102 };103 104  the intMain ()106 {107 108Std::vector<str> str_vec{"xa","Sad","","","","Qqewhegr","AQDQ"};109  the 111std::function<BOOL(ConstSTR &) > fn = &Str::empty; the 113std::size_t empty_size_function=std::count_if (Str_vec.begin (), Str_vec.end (), FN); the  thestd::size_t empty_size_bind=std::count_if (Str_vec.begin (), Str_vec.end (), Std::bind (&str::empty,std::p laceholders::_1)); the 117std::size_t empty_size_mem_fn=std::count_if (Str_vec.begin (), Str_vec.end (), STD::MEM_FN (&str::empty));118 119  -Std::cout << empty_size_function <<Std::endl;121Std::cout << Empty_size_bind <<Std::endl;122Std::cout << EMPTY_SIZE_MEM_FN <<Std::endl;123 124  the 126std::size_t size = std::count_if (Str_vec.begin (), Str_vec.end (), [] (Conststr& str) {returnstr.empty ();});127Std::cout << Size <<Std::endl; - 129  the     return 0;131}

C + + class member function pointer class member data pointer