"03" pointer, return value, const of member function

1 //2 //2015-03-05 03/553 //const of pointers, return values, member functions4 //5 6#include <iostream>7#include <string>8 9 using namespacestd;Ten  One // ------------------------------ A //1. The const of the pointer - // ------------------------------ - Const Char*P1 ="Hello";//P is pointing to a constant the Char*ConstP2 ="Hello";//p itself is a constant - Const Char*ConstP3 ="Hello";//p itself is a constant, pointing to a constant -  - // ------------------------------ + //2. Const of the return value - // ------------------------------ + stringfoo () A { at     return "Hello"; - } -  - intMainintargcChar*argv[]) - { -     //The following is legal, changing the declaration of Foo to const string foo () in     //is no longer legal, declaring the return as const avoids the ' = = ' error as ' = '.  -Foo () ="ABC"; to     return 0; + } -  the // ------------------------------ * //3. Const for member functions $ // ------------------------------Panax Notoginseng classBar - { the  Public: +     voidfunc () A{cout <<"non-const func is called"; } the  +     voidFunc ()Const -{cout <<"The const Func is called"; } $  $     //The const property of member functions can be overloaded, and we know that non-static member functions imply this pointer, -     //All const and NON-CONST member functions can be understood as the following declaration: -     //void func (bar *this); (1) the     //void func (const bar *this); (2) -     //a Non-const object that can call (1) & (2), and a const object can only be called (2). Wuyi }; the  - intMainintargcChar*argv[]) Wu { -     //This is a bar* type and can be assigned to const . About     //follow the Non-const-const match call, if no $     //define the Non-const version, then you can call the Const.  - Bar B; - B.func (); -  A     //only the const version is called, this is the const bar* type.  +     ConstBar CB; the Cb.func (); - } $  the // ---------------------------------------------- the //4. Code redundancy due to const overloading of member functions the // ---------------------------------------------- the classTextBlock - { in  Public: theTextBlock (): Text ("Hello") the     {} About  the     //Const version the     Const Char&operator[](Constsize_t POS)Const the     { +cout <<"The const operator[] is called"<<Endl; -         returnText[pos]; the     }Bayi  the     //version Non-const can call the const version the     Char&operator[](Constsize_t POS) -     { -cout <<"Non-const operator[] is called"<<Endl; the         returnconst_cast<Char&>( thestatic_cast<ConstTextblock&> (* This) [POS] the             ); the     } - Private: the     stringtext; the }; the 94 intMainintargcChar*argv[]) the { the TextBlock TB; thetb[1] ='J';//OK Call Non-const98      About     ConstTextBlock CTB; -cout << ctb[1] <<Endl;101 102     //The Error return type is a const reference and cannot be assigned a value. 103     //in fact, if you simply return the simple variable char f (), you cannot assign a value. 104ctb[1] ='H'; the }106 107 // ----------------------------------------------108 //5. Use of mutable109 // ---------------------------------------------- the classTextBlock111 { the  Public:113TextBlock (): Text ("Hello"), Lengthvalid (false) the     {} the  thesize_t Length ()Const   //here size_t is a simple type and returns without setting a const. 117     {118         if(!lengthvalid)119         { -TextLength =strlen (text);121Lengthvalid =true;122         }123         returntextLength;124     } the Private:126     Char*text;127mutableBOOLLengthvalid; - mutable size_t textLength;129};

"03" pointer, return value, const of member function