Precedence between member access from a pointer and cast

问题

If I have

 typedef struct{
       int i;
 } typeB;

 typeA *p;

then: What is the precedence between member access from a pointer and cast?

 (typeB *)p->i

Is it actually ((typeB *)p)->i or (typeB *)(p->i)?

回答1:

An operator precedence table would show that a -> binds more tightly than the cast.

typedef void *typeA;
typeB b;
typeA a = &b;
(typeB *)a->i;   /* wrong: attempt to dereference a void pointer */
((typeB *)a)->i; /* ok */

A complete operator precedence table for your future reference is provided below. In the table, operators higher in the list bind more tightly than operators lower in the list (so the Primary Expression Operators bind the most tightly). If operators of the same precedence are used in the same expression in an ambiguous way (that is, not captured within a Primary Expression Operator like () or []), then it is resolved by following the associativity direction. So, for example the expression:

7 + (3 - 5 * 2 + 15) - 6

is evaluated in this order (according to the table):

7 + (3 - 10 + 15) - 6     // evaluate * in ()
7 + (-7 + 15) - 6         // evaluate - in () (it is left of the +)
7 + 8 - 6                 // evaluate + in ()
15 - 6                    // evaluate + (it is left of the -)
9                         // evaluate -

Of course, the compiler is free to perform the computation differently, but its result must match the result obtained when following the precedence rules.

Operator Type   Operator(s)                                     Associativity
=============   ===========                                     =============
Primary         () [] . -> expr++ expr--                        left-to-right
Expression 
Operators       
-------------   -----------                                     -------------
Unary           * & + - ! ~ ++expr --expr (typecast) sizeof     right-to-left
Operators       
-------------   -----------                                     -------------
Binary          * / %                                           left-to-right
Operators       + -
                >> <<
                < > <= >=
                == !=
                &
                ^
                |
                &&
                ||
-------------   -----------                                     -------------
Ternary         ?:                                              right-to-left
Operator
-------------   -----------                                     -------------
Assignment      = += -= *= /= %= >>= <<= &= ^= |=               right-to-left
Operators       
-------------   -----------                                     -------------
Comma           ,                                               left-to-right
=============   ===========                                     =============

回答2:

in C, -> operatior's precedence is higher than cast , which is (type name)

so (typeB *)p->i is (typeB *)(p->i)

来源：https://stackoverflow.com/questions/17077628/precedence-between-member-access-from-a-pointer-and-cast

标签

casting

operator-precedence