const pointer

经常容易混淆的概念

pointer to const -> 指向的数据不能被修改

const pointer -> 指针的地址不能被修改

int a = 3;
int b = 4;

// read from right to left
const int * p1 = &a;  // a pointer to a const int
int * const p2 = &b;  // a const pointer to an int

*p1 = b; // not OK
p1 = &b; // OK
a = 4; // OK: *p1 = 4

p2 = &a; // not OK
*p2 = a; // OK

reference: http://www.cnblogs.com/haox/p/3177726.html