Summary on "const" in C++

"const" is a very common key word in C++ programming language. I use lots of "const" in my previous project and now I want to write some summary about the usage of it.

I suppose there is a Class "A".

const with "Pointer"
1. const A * a : it's a pointer to const class A. You can change the pointer a, but you cannot change the data it points to.
2. A const *a : it's the same to the usage of 1.
3. A * const a: it's a constant pointer to class A. You can change the data pointer a points to , but you can change the pointer.
const with "Call by reference"
1. const A &a: object a cannot be modified.
2. A const &a: it's the same to the usage of 1.
3. A & const a: It's a not recmmended usage! ( visual studio: warning C4227: anachronism used : qualifiers on reference are ignored!)
const with normal usage
1. const int i;
2. int const i;
the usage of 1 and 2 is the same.

One Example:

class A
{
public:
    int val;
};
void test1( A  & const a)
{
    A aa;
    aa.val = 2;
    a = aa;   // warning C4227: anachronism used : qualifiers on reference are ignored
}
void test2(const A  &  a)
{
    A aa;
    aa.val = 3;
    a = aa;  // error C2678: binary '=' : no operator found which takes a left-hand operand of type 'const A' (or there is no acceptable conversion)
}
void main()
{
    A aa;
    test1(aa);
    test2(aa);
A aaa;
aaa.val =4;
A &amp; const bbb=aaa;   // warning C4227: anachronism used : qualifiers on reference are ignored

}

Thanks!

Reference:

[1]. http://www.devmaster.net/forums/archive/index.php/t-3863.html [2]. http://faq.csdn.net/read/2143.html