In C++, this pointer is passed as a hidden argument to all non-static member function calls. The type of this depends upon function declaration. If the member function of a class X is declared const, the type of this is const X* (see code 1 below), if the member function is declared volatile, the type of this is volatile X* (see code 2 below), and if the member function is declared const volatile, the type of this is const volatile X* (see code 3 below).

　　Code 1

1 #include
2 class X
3 {
4 void fun() const
5 {
6 // this is passed as hidden argument to fun().
7 // Type of this is const X*
8 }
9 };

　　Code 2

1 #include
2 class X
3 {
4 void fun() volatile
5 {
6 // this is passed as hidden argument to fun().
7 // Type of this is volatile X*
8 }
9 };

　　Code 3

1 #include
2 class X
3 {
4 void fun() const volatile
5 {
6 // this is passed as hidden argument to fun().
7 // Type of this is const volatile X*
8 }
9 };

　　补充：

　　（1）In an ordinary nonconst member function, the type of this is a const pointer to the class type. We may change the value to which this points but cannot change the address that this holds. In a const member function, the type of this is a const pointer to a const class - type object. We may change neither the object to which this points nor the address that this holds.

　　（2）What is the purpose of a volatile member function in C++?【from stackoverflow】

　　

　　References:http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1905.pdf

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　　2013-11-26　　09:32:58