Valid tive C ++ Clause 3: Use const whenever possible

Const modifier pointer: If the keyword const appears on the left side of asterisk *, it indicates that the indicated object is a constant. If const appears on the right side of *, it indicates that the pointer itself is a constant, if it appears on both sides, it indicates that the things and pointers are constants;

Const STD: vector <int>: iterator iter = Vec. Begin (); // The role of ITER is like T * const; ++ ITER; Error

STD: vector <int >:: const_iterator citer = VEC. Begin (); // The role of citer is like a const T *; * citer = 10; Error

Const modifier function return value: declare operator *'s return value as const type to avoid (A * B) = C; this meaningless value assignment action

Const member function: indicates that the member function can act on the const object.

The two member functions have different constants and can be overloaded.

Bitwise constness: the const member function cannot change any non-static member variable of the object.

Class ctextblock {

Public:

STD: size_t length () const;

PRIVATE:

Char * ptext;

SDT: size_t textlength;

Bool lengthvalid;

};

 

STD: size_t ctextblock: length () const

{

If (! Lengthisvalid)

{

Textlength = STD: strlen (ptext); // error! You cannot assign a value to a const member function.

Lengthisvalid = ture; // textlength and lengthvalid

}

}

In this case, you can use a const-related swing field: mutable (variable) to release the bitwise constness constraint of the non-static member variable.

Class ctextblock {

Public:

STD: size_t length () const;

PRIVATE:

Char * ptext;

Mutable SDT: size_t textlength;

Mutable bool lengthvalid;

};

STD: size_t ctextblock: length () const

{

If (! Lengthisvalid)

{

Textlength = STD: strlen (ptext); // now textlength can be changed

Lengthisvalid = ture; // and lengthvalid

}

}

Avoid duplication in const member functions and non-const member functions: Call the const brother using non-const for two conversions. The reverse method should not be that the const member function does not change the logical state of the object.

Class textblock {

Public:

Const char & operator [] (STD: size_t position) const

{

......

Return text [opsition];

}

Char & operator [] (STD: size_t position)

{

Return

Const_cast <char &> (// remove the const of the return value of OP []

Static_cast <const textblock &> (* This) [] // call op [] to add const to * This

);

}

};