2017_11_06-const_in_cpp

const pointer

乔俊峰 Junfeng Qiao， 2017-11-06

最近看到了一篇很好的文章，终于搞清楚了const的用法。
现将重点摘抄如下：

1. Every declaration in C and C++ has two
   principal parts: a sequence of zero or more
   declaration specifiers, and a sequence of
   one or more declarators, separated by
   commas.

   static unsigned long int *x[N];

   declaration specifiers: static unsigned long int

   declarator: *x[N];

   注意*是declarator

2. The operators in a declarator group according
   to the same precedence as they do when
   they appear in an expression.

   所以[N]先与x结合，再与*结合，x is an “array of N elements of
   pointer to …” something

3. Parentheses serve two roles in
   declarators: first, as the function call
   operator, and second, as grouping. As
   the function call operator, ()have the
   same precedence as []. As grouping,
   () have the highest precedence of all.

   *f(int) is a declarator
   specifying that f is a “function …
   returning a pointer … .” In contrast,
   (*f)(int) specifies that f is a “pointer
   to a function … .”

4. A declarator may contain more
   than one identifier. The declarator
   *x[N] contains two identifiers, x and N.
   Only one of those identifiers is the
   one being declared, and it’s called the
   declarator-id. The other(s), if any,
   must have been declared previously.

   x is declarator-id

5. Type specifiers contribute to the type of the
   declarator-id; other specifiers provide nontype
   information that applies directly to the
   declarator-id.

   static unsigned long int *x[N];
unsigned long int is type specifiers.

6. The keywords const and volatile are
   type specifiers.

7. The order in which the declaration specifiers
   appear in a declaration doesn’t matter.

8. The only declaration specifiers that can also
   appear in declarators are const and volatile.

9. pointer declarations read from right-to-left.
   Always write const and volatile to the right.

   T const *p;
T *const p;

10. Recognizing the boundary between
    the last declaration specifier and the
    declarator is one of the keys to understanding
    declarations.

    Use const int *p;
    rather than const int* p;

文章地址：

http://www.dansaks.com/articles/1999-02%20const%20T%20vs%20T%20const.pdf