About the array subscripting operator

问题

Quoting from the C11 standard :

Array subsripting (§ 6.5.2.1)

The definition of the subscript operator [] is that E1[E2] is identical to (*((E1)+(E2))).

I would like to know why are the brackets around E1 necessary (they were missing in the C89 standard), ie in which expression can (*(E1+(E2))) be different from (*((E1)+(E2))) ?

回答1:

According to http://www.open-std.org/jtc1/sc22/wg14/www/docs/n841.htm, it is inserted just for clarity. The two expressions are the syntatically equivalent.

Public Comment Number PC-UK0103
Comment 1.
Category: Editorial change/non-normative contribution
Committee Draft subsection: 6.3.2.1
Title: Array subscripting example
Detailed description:

Paragraph 2 should replace "(*(E1+(E2)))" by "(*((E1)+(E2)))", to avoid confusion. Yes, I know that the syntactic chart makes it quite unambiguous, but the current wording in paragraph 2 is very confusing.

来源：https://stackoverflow.com/questions/12201210/about-the-array-subscripting-operator