首先看看是怎么定义的
http://en.cppreference.com/w/cpp/language/operator_precedence
The following table lists the precedence and associativity of C++ operators. Operators are listed top to bottom, in descending precedence.
| Precedence | Operator | Description | Associativity |
|---|---|---|---|
| 1 | :: |
Scope resolution | Left-to-right |
| 2 |
++ --
|
Suffix/postfix increment and decrement | |
() |
Function call | ||
[] |
Array subscripting | ||
. |
Element selection by reference | ||
−> |
Element selection through pointer | ||
| 3 |
++ --
|
Prefix increment and decrement | Right-to-left |
+ −
|
Unary plus and minus | ||
! ~
|
Logical NOT and bitwise NOT | ||
(type) |
Type cast | ||
* |
Indirection (dereference) | ||
& |
Address-of | ||
sizeof |
Size-of | ||
new, new[]
|
Dynamic memory allocation | ||
delete, delete[]
|
Dynamic memory deallocation | ||
| 4 |
.* ->*
|
Pointer to member | Left-to-right |
| 5 |
* / %
|
Multiplication, division, and remainder | |
| 6 |
+ −
|
Addition and subtraction | |
| 7 |
<< >>
|
Bitwise left shift and right shift | |
| 8 |
< <=
|
For relational operators < and ≤ respectively | |
> >=
|
For relational operators > and ≥ respectively | ||
| 9 |
== !=
|
For relational = and ≠ respectively | |
| 10 | & |
Bitwise AND | |
| 11 | ^ |
Bitwise XOR (exclusive or) | |
| 12 | | |
Bitwise OR (inclusive or) | |
| 13 | && |
Logical AND | |
| 14 | || |
Logical OR | |
| 15 | ?: |
Ternary conditional | Right-to-left |
= |
Direct assignment (provided by default for C++ classes) | ||
+= −=
|
Assignment by sum and difference | ||
*= /= %=
|
Assignment by product, quotient, and remainder | ||
<<= >>=
|
Assignment by bitwise left shift and right shift | ||
&= ^= |=
|
Assignment by bitwise AND, XOR, and OR | ||
| 16 | throw |
Throw operator (for exceptions) | |
| 17 | , |
Comma | Left-to-right |
还有一个问题，就是设计到成员和括号的时候：
如 dgif_lib.c中 有这么一段：
#define READ(_gif,_buf,_len) \
(((GifFilePrivateType*)_gif->Private)->Read ? \
((GifFilePrivateType*)_gif->Private)->Read(_gif,_buf,_len) : \
fread(_buf,1,_len,((GifFilePrivateType*)_gif->Private)->File))
<转>如何记忆两种结合性和15种优先级？下面讲述一种记忆方法。
结合性有两种，一种是自左至右，另一种是自右至左，大部分运算符的结合性是自左至右，只有单目运算符、三目运算符的赋值运算符的结合性自右至左。优先级有15种。记忆方法如下：
记住一个最高的：构造类型的元素或成员以及小括号。
记住一个最低的：逗号运算符。
剩余的是一、二、三、赋值。
意思是单目、双目、三目和赋值运算符。
在诸多运算符中，又分为：
算术、关系、逻辑。
两种位操作运算符中，移位运算符在算术运算符后边，逻辑位运算符在逻辑运算符的前面。再细分如下：
算术运算符分 *，/，%高于+，-。
关系运算符中，》，》=，《，〈=高于==，！=。
逻辑运算符中，除了逻辑求反（！）是单目外，逻辑与（&&）高于逻辑或（||）。
逻辑位运算符中，除了逻辑按位求反（~）外，按位与（&)高于按位半加（^)，高于按位或（|）。
这样就将15种优先级都记住了，再将记忆方法总结如下：
去掉一个最高的，去掉一个最低的，剩下的是一、二、三、赋值。双目运算符中，顺序为算术、关系和逻辑，移位和逻辑位插入其中。
(GifFilePrivateType*)_gif->Private 所以这里先有_gif->Private，然后做强制转化--上表中第一大优先级(Type cast)。