C ++ class uses constructor to initialize the differences between class tables and assignment in the constructor body

C ++ Primer:

 

// Constref. cpp: defines console applicationsProgram.
//

# Include "stdafx. H"

Class constref
{
Public:
Constref (int ii );

Int I;
Const int ci;
Int & Ri;
};

Constref: constref (int ii)
{
I = II;
Ci = II;
Ri = I;
}

// Constref: constref (int ii): I (ii), CI (I), RI (ii ){}

Int _ tmain (INT argc, _ tchar * argv [])
{
Constref B (5 );

Printf ("% d, % d, % d", B. I, B. CI, B. RI );
Return 0;
}

In this case, there is an error in writing. Error c2758: "constref: Ci": it must be initialized in the constructor base/member Initial Value Setting item list;
Constref: RI: Must be initialized in the constructor base/member Initial Value List;
Error c2166: Specify the const object with the left value;

 

However

Constref: constref (int ii)
{
I = II;
Ci = II;
Ri = I;
}

Replace constref: constref (int ii): I (ii), CI (I), RI (ii) {} correctly. Do you know why?

 

Remember: const objects can be initialized or referenced objects, but they cannot be assigned a value. Initialization must be completed before you start executing the constructor's function body. The only opportunity to initialize a const or referenced data member is in the constructor initialization list.