Something Conclusion in C++

Object

• Most generally, an object is a region of memory that has type.

const Qualifier

• "const type object" means object's type is type, and object is const. 由内而外的解析.

int ivar = 2;
typedef int *PI;

// the type of pi is PI = (int*), and pi is const
const PI pi = &ivar;

// pi is a pointer, the type of (*pi) is int, and (*pi) is const
const int *pi;

// pi is const, pi is a pointer, the type of (*pi) is int, and (*pi) is const
const int *const pi = &ivar;

• const reference

A const reference may be bound to an object of a different but related type or to an rvalue.

• Names defined outside any functions have global scope.

When we define a non-const variable at global scope, it is accessible throughout the program. Unless specified using extern, const variables declared at global scope are local to a file by default. (So const variables can be defined in header files.)

• const member function

That 'const' modifies the type of the implicit 'this' parameter.

class A {
public:
    int m_ivar;
    A():m_ivar(1024) {}
    ~A(){}
    int get() const {
        return m_ivar;
    }
};

int main()
{
    A insA;
    // insA.get( const A *const this)
    insA.get();
    return 0;
}

这样也就解释了：成员函数的重载需要考虑const或volatile，因为这样改变了隐藏参数this的类型。

array

• sizeof 返回一个 ‘对象的类型’ 或 ‘类型名’ 的长度，长度的单位是字节数，sizeof表达式的结果是编译时的常量。