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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,69 +1,152 @@ | ||
| //============================================================================ | ||
| // Name : PointerToMember.cpp | ||
| // Author : joergboe | ||
| // Version : | ||
| // Copyright : Your copyright notice | ||
| // Description : Hello World in C++, Ansi-style | ||
| //============================================================================ | ||
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| #include <iostream> | ||
| using namespace std; | ||
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| class Base { | ||
| public: | ||
| char a; | ||
| char b; | ||
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| Base(char a_, char b_) : a(a_), b(b_) {}; | ||
| void print1(int val) { | ||
| cout << "print1 a=" << a << " b=" << b << " val=" << val << endl; | ||
| char const * mess; | ||
| char a, b; | ||
| char const cc; | ||
| private: | ||
| char privc; | ||
| public: | ||
| Base(char const * mess_ = "Base", char a_ = 'a', char b_ = 'b') : mess(mess_), a(a_), b(b_), cc('C'), privc('p') {}; | ||
| void print1(int val) const { | ||
| cout << "print1"; | ||
| printVars(); | ||
| cout << " val=" << val << endl; | ||
| } | ||
| /*void print2(int val) const { | ||
| cout << "print2"; | ||
| printVars(); | ||
| cout << " val=" << val << endl; | ||
| }*/ | ||
| void setA(char c_) { | ||
| a = c_; | ||
| } | ||
| void setB(char c_) { | ||
| b = c_; | ||
| } | ||
| void print2(int val) { | ||
| cout << "print2 a=" << a << " b=" << b << " val=" << val << endl; | ||
| protected: | ||
| void printVars() const { | ||
| cout << " mess=" << mess << " a=" << a << " b=" << b << " privc=" << privc; | ||
| } | ||
| }; | ||
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| class Derived : public Base { | ||
| public: | ||
| char c; | ||
| Derived(int a_, int b_) : Base(a_, b_), c('@') {}; | ||
| char d; | ||
| Derived() : Base("Derived", 'a'), d('d') {}; | ||
| void print3(int val) { | ||
| cout << "print3 a=" << a << " b=" << b << " c=" << c << " val=" << val << endl; | ||
| cout << "print3"; | ||
| printVars(); | ||
| cout << " d=" << d << endl; | ||
| } | ||
| }; | ||
|
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| typedef char Base::* MemberPointer; | ||
| typedef char Base::* MemberPointerB1; | ||
| //using MemberPointer = char Base::*; //c11 stype | ||
| typedef void (Base::*MethodPointer)(int); | ||
| //using MethodPointer = void (Base::*)(int); | ||
|
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| int main() { | ||
| cout << "!!!Hello World!!!" << endl; | ||
| Base object1('a', 'b'); | ||
| object1.print1(55); | ||
| object1.print2(56); | ||
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| //Member Pointer | ||
| char Base::* const memberPointer1 = &Base::a; //direct declaration (const) | ||
| object1.*memberPointer1 = 'A'; | ||
| MemberPointer memberPointer2 = &Base::b; | ||
| object1.*memberPointer2 = 'B'; //declaration using alias (typedef / using | ||
| //Method Pointer | ||
| void (Base::*methodPointer1)(int) = &Base::print1; //direct declaration | ||
| Base* objectPtr = &object1; | ||
| (objectPtr->*methodPointer1)(11); | ||
| MethodPointer methodPointer2 = &Base::print2; | ||
| (object1.*methodPointer2)(22); | ||
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| //Derived | ||
| Derived object2('x','y'); | ||
| void (Derived::* methodPointer3)(int) = &Derived::print3; | ||
| (object2.*methodPointer3)(22); | ||
| methodPointer3 = &Derived::print1; | ||
| (object2.*methodPointer3)(100); | ||
| (object2.*methodPointer1)(0); //use method pointer of Base with object type Derived | ||
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| cout << "sizeof(object1)=" << sizeof(object1) << endl; | ||
| cout << "sizeof(object2)=" << sizeof(object2) << endl; | ||
| cout << "Demonstration of pointer to member and pointer to method.\n" | ||
| "The declaration 'T C::* P' declares P as a pointer to non-static member of C of type T.\n" | ||
| "Where member can be a non-static attribute or a non-static class function.\n" | ||
| "Use operator '.*' (pointer to member of object) or '->*' (pointer to member of pointer)\n" | ||
| "to access these members.\n" | ||
| "Address operator '&C::member delivers the address for these pointers.\n" | ||
| "Pointers to member must not be assigned to other pointer types an void*.\n" | ||
| "The 'nullptr' can be assigned to a pointer to member.\n\n"; | ||
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| Base base1; | ||
| base1.print1(1); | ||
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| cout << "\n****** Pointer to class member (non-static member) ******\n"; | ||
| cout << "use 'char Base::* const char_ptr1' to declare a pointer to member\n"; | ||
| cout << "use '&Base::a' to define the pointer\n"; | ||
| char Base::* char_ptr1 = &Base::a; | ||
| cout << "use 'base1.*char_ptr1' to address where it points to.\n"; | ||
| cout << base1.*char_ptr1 << endl; | ||
| cout << "char_ptr1 may point to all non-const char members of Base\n"; | ||
| char_ptr1 = &Base::b; | ||
| cout << base1.*char_ptr1 << endl; | ||
| cout << "The member must be visible in that context:\n"; | ||
| //char_ptr1 = &Base::privc; //error: ‘char Base::privc’ is private within this context | ||
| cout << "the pointer can be const qualified with 'char Base::* const char_ptr2 = &Base::a'\n"; | ||
| char Base::* const char_ptr2 = &Base::a; | ||
| cout << "base1.*char_ptr2: " << base1.*char_ptr2 << endl; | ||
| cout << "constantness is maintained\n"; | ||
| //char_ptr2 = &Base::b; //error: assignment of read-only variable ‘char_ptr2’ | ||
| //char_ptr1 = &Base::cc; //error: invalid conversion from ‘const char Base::*’ to ‘char Base::*’ [-fpermissive] | ||
| Base const base2("Base const"); | ||
| //base2.*char_ptr1 = 'x'; //error: assignment of read-only location ‘*(((const char*)(& base2)) + ((sizetype)char_ptr1))’ | ||
| const char * Base::* mess_ptr = &Base::mess; | ||
| cout << "base2.*mess_ptr: " << base2.*mess_ptr << endl; | ||
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| cout << "\nPointer to members can be used with objects of public derived classes\n"; | ||
| Derived derived1; | ||
| cout << "derived1.*mess_ptr: " << derived1.*mess_ptr << endl; | ||
| cout << "But pointers to members of derived can not point to members of base\n"; | ||
| char Derived::* char_ptr3 = &Derived::d; | ||
| cout << "derived1.*char_ptr3: " << derived1.*char_ptr3 << endl; | ||
| //base1.*char_ptr3 = 'x'; //error: pointer to member type ‘char’ incompatible with object type ‘Base’ | ||
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| cout << "\nRecomended use of aliases:\n"; | ||
| typedef char Base::* BaseToCharMemberPtr; | ||
| using BaseToMessMemberPtr = char const * Base::*; //c11 stype | ||
| BaseToCharMemberPtr mptr3 = &Base::b; | ||
| BaseToMessMemberPtr mptr4 = &Base::mess; | ||
| cout << "base2.*mptr4: " << base2.*mptr4 << " base2.*mptr3: " << base2.*mptr3 << endl; | ||
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| cout << "\nUse operator '->*' with an object pointer\n"; | ||
| Base const * b_cptr = & base2; | ||
| cout << "b_cptr->*mptr4: " << b_cptr->*mptr4 << " b_cptr->*mptr3: " << b_cptr->*mptr3 << endl; | ||
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| cout << "\n****** Pointer to class member functions (non-static member) ******\n"; | ||
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| cout << "Function pointer declaration rules and '::*' declares a pointer to a visible member function:\n" | ||
| "void (Base::*func_ptr1)(char) = &Base::setA\n"; | ||
| void (Base::*func_ptr1)(char) = &Base::setA; | ||
| cout << "the usage of this pointer requires parentheses:\n"; | ||
| (base1.*func_ptr1)('x'); | ||
| cout << "a pointer of this type can point to any member function with a matching signature.\n"; | ||
| func_ptr1 = &Base::setB; | ||
| (base1.*func_ptr1)('y'); | ||
| base1.print1(12); | ||
| cout << "The member must be visible in that context:\n"; | ||
| //void (Base::*func_ptr2)() = &Base::printVars; //error: ‘void Base::printVars()’ is protected within this context | ||
| cout << "\nPointer to members can be used with objects of public derived classes\n"; | ||
| (derived1.*func_ptr1)('z'); | ||
| derived1.print1(0); | ||
| cout << "const qualifier is part of the function pointer type:\n"; | ||
| void (Base::*func_ptr_const)(int) const = &Base::print1; | ||
| cout << "type func_ptr1: " << typeid(func_ptr1).name() << | ||
| "\ntype func_ptr_const: " << typeid(func_ptr_const).name() << endl; | ||
| cout << "Use with a pointer to object (b_cptr->*func_ptr_const)(14)\n"; | ||
| (b_cptr->*func_ptr_const)(14); | ||
| Derived * d_ptr = & derived1; | ||
| (d_ptr->*func_ptr_const)(15); | ||
|
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| cout << "\nRecomended use of aliases:\n"; | ||
| typedef void (Base::*BaseSetCharMemberFunctionPointer)(char); | ||
| using BasePrintMemberFunctionPointer = void (Base::*)(int) const; | ||
| BaseSetCharMemberFunctionPointer fmp1 = &Base::setA; | ||
| BasePrintMemberFunctionPointer fmp2 = &Base::print1; | ||
| (base1.*fmp1)('@'); | ||
| (base1.*fmp2)(999); | ||
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| cout << "\n****** pointer to member and pointer ******\n" | ||
| "Pointer to member can not be assigned to a 'void *'\n"; | ||
| // void * vptr = func_ptr1; //error: cannot convert ‘void (Base::*)(char)’ to ‘void*’ in initialization | ||
| cout << "Can assign 'nullptr' to pointer to member but never use such member! The result is undefined.\n"; | ||
| char_ptr1 = nullptr; | ||
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| cout << "END" << endl; | ||
|
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| return 0; | ||
| } |