C++中指针笔记

The declaration:

const char *answer_ptr = "Forty-Two";

does not tell C++ that the variable answer_ptr is a constant. Instead it tells C++ that the data pointed to by answer_ptr is a constant. The data cannot be changed, but the pointer can. Again we need to make sure we know the difference between "things" and "pointers to things."

What's answer_ptr? A pointer. Can it be changed? Yes, it's just a pointer. What does it point to? A const char array. Can the data pointed to by answer_ptr be changed? No, it's constant.

If you put the const after the *, you tell C++ that the pointer is constant. For example:

char *const name_ptr = "Test";

What's name_ptr? A constant pointer. Can it be changed? No. What does it point to? A character. Can the data we pointed to by name_ptr be changed? Yes.

Finally, we put const in both places, creating a pointer that cannot be changed to a data item that cannot be changed:

const char *const title_ptr = "Title";

One way of remembering whether the const modifies the pointer or the value is to remember that *const reads "constant pointer" in English.