C ++ keyword mutable

Mutable

(1) mutable means "variable, variable", which is the opposite of const in C ++.

(2) In C ++, mutable is also set to break through the const restrictions. Variables modified by mutable will always be in a mutable state, even in a const Function

Instance description:

 # include 
   
   
 
    using  
    namespace  STD; 
   
 
    class  tew.utable 
   
{< br> 
    Public :< br> tew.utable () {I = 
    0 ;}< br> 
    int  output () 
    const  
   
{< br> 
    return  I ++; 
    //  
    error c2166: l-value specifies const object  
    
 }< br> 
    private : 
   
 
    int  I; 
   
 }; 
   
 
    int  main () 
   
{< br> tew.utable; 
   
 cout 
    
     return  
     0 ;< BR >}
   
  

Obviously, I ++ cannot compile the const modifier function.

 
# Include <iostream>
Using NamespaceSTD;

ClassTestmutable
{
Public:
Testmutable () {I =0;}
IntOutput ()Const
{
ReturnI ++;
}
Private:
MutableIntI;
};

IntMain ()
{
Testmutable;
Cout <testmutable. Output () <Endl;
Return 0;
}
 

After mutable is added to int I, the compilation is passed, and the function of the keyword mutable can be seen immediately.