c语言操作符的优先级

　c语言的操作符共有15个优先级，如下：

　　Operators Associativity

　　() [] -> . left to right

　　! ~ ++ -- + - * (type) sizeof right to left

　　* / % left to right

　　+ - left to right

　　<< >> left to right

　　< <= > >= left to right

　　== != left to right

　　& left to right

　　^ left to right

　　| left to right

　　&& left to right

　　|| left to right

　　?: right to left

　　= += -= *= /= %= &= ^= |= <<= >>= right to left

　　, left to right

　　优先级从上到下依次递减，最上面具有最高的优先级，逗号操作符具有最低的优先级。

　　所有的优先级中，只有三个优先级是从右至左结合的，它们是单目运算符、条件运算符、赋值运算符。其它的都是从左至右结合。

　　具有最高优先级的其实并不算是真正的运算符，它们算是一类特殊的操作。()是与函数相关，[]与数组相关，而－>及.是取结构成员。

　　其次是单目运算符，所有的单目运算符具有相同的优先级，因此在我认为的 真正的运算符中它们具有最高的优先级，又由于它们都是从右至左结合的，因此*p++与*(p++)等效是毫无疑问的。

　　接下来是算术运算符，*、/、%的优先级当然比+、－高了。

　　移位运算符紧随其后。

　　其次的关系运算符中，< <= > >=要比 == !=高一个级别，不大好理解。

　　所有的逻辑操作符都具有不同的优先级（单目运算符出外，！和~）

　　逻辑位操作符的"与"比"或"高，而"异或"则在它们之间。

　　跟在其后的&&比||高。

　　接下来的是条件运算符，赋值运算符及逗号运算符。

　　在C语言中，只有4个运算符规定了运算方向，它们是&&、| |、条件运算符及赋值运算符。

　　&&、| |都是先计算左边表达式的值，当左边表达式的值能确定整个表达式的值时，就不再计算右边表达式的值。如 a = 0 && b; &&运算符的左边位0，则右边表达式b就不再判断。

　　在条件运算符中。如a?b:c；先判断a的值，再根据a的值对b或c之中的一个进行求值。

　　赋值表达式则规定先对右边的表达式求值，因此使 a = b = c = 6;成为可能。

　　C++运算符优先级

　　

Operator	Description	Example	Overloadable
Group 1 (no associativity)
::	Scope resolution operator	Class::age = 2;	NO
Group 2
()	Function call	isdigit('1')	YES
()	Member initalization	c_tor(int x, int y) : _x(x), _y(y*10){};	YES
[]	Array access	array[4] = 2;	YES
->	Member access from a pointer	ptr->age = 34;	YES
.	Member access from an object	obj.age = 34;	NO
++	Post-increment	for( int i = 0; i < 10; i++ ) cout << i;	YES
--	Post-decrement	for( int i = 10; i > 0; i-- ) cout << i;	YES
const_cast	Special cast	const_cast<type_to>(type_from);	NO
dynamic_cast	Special cast	dynamic_cast<type_to>(type_from);	NO
static_cast	Special cast	static_cast<type_to>(type_from);	NO
reinterpret_cast	Special cast	reinterpret_cast<type_to>(type_from);	NO
typeid	Runtime type information	cout « typeid(var).name(); 　　cout « typeid(type).name();	NO
Group 3 (right-to-left associativity)
!	Logical negation	if( !done ) …	YES
not	Alternate spelling for !
~	Bitwise complement	flags = ~flags;	YES
compl	Alternate spelling for ~
++	Pre-increment	for( i = 0; i < 10; ++i ) cout << i;	YES
--	Pre-decrement	for( i = 10; i > 0; --i ) cout << i;	YES
-	Unary minus	int i = -1;	YES
+	Unary plus	int i = +1;	YES
*	Dereference	int data = *intPtr;	YES
&	Address of	int *intPtr = &data;	YES
new	Dynamic memory allocation	long *pVar = new long; 　　MyClass *ptr = new MyClass(args);	YES
new []	Dynamic memory allocation of array	long *array = new long ;	YES
delete	Deallocating the memory	delete pVar;	YES
delete []	Deallocating the memory of array	delete [] array;	YES
(type)	Cast to a given type	int i = (int) floatNum;	YES
sizeof	Return size of an object or type	int size = sizeof floatNum; 　　int size = sizeof(float);	NO
Group 4
->*	Member pointer selector	ptr->*var = 24;	YES
.*	Member object selector	obj.*var = 24;	NO
Group 5
*	Multiplication	int i = 2 * 4;	YES
/	Division	float f = 10.0 / 3.0;	YES
%	Modulus	int rem = 4 % 3;	YES
Group 6
+	Addition	int i = 2 + 3;	YES
-	Subtraction	int i = 5 - 1;	YES
Group 7
<<	Bitwise shift left	int flags = 33 << 1;	YES
>>	Bitwise shift right	int flags = 33 >> 1;	YES
Group 8
<	Comparison less-than	if( i < 42 ) …	YES
<=	Comparison less-than-or-equal-to	if( i <= 42 ) ...	YES
>	Comparison greater-than	if( i > 42 ) …	YES
>=	Comparison greater-than-or-equal-to	if( i >= 42 ) ...	YES
Group 9
==	Comparison equal-to	if( i == 42 ) ...	YES
eq	Alternate spelling for ==
!=	Comparison not-equal-to	if( i != 42 ) …	YES
not_eq	Alternate spelling for !=
Group 10
&	Bitwise AND	flags = flags & 42;	YES
bitand	Alternate spelling for &
Group 11
^	Bitwise exclusive OR (XOR)	flags = flags ^ 42;	YES
xor	Alternate spelling for ^
Group 12
|	Bitwise inclusive (normal) OR	flags = flags | 42;	YES
bitor	Alternate spelling for |
Group 13
&&	Logical AND	if( conditionA && conditionB ) …	YES
and	Alternate spelling for &&
Group 14
||	Logical OR	if( conditionA || conditionB ) ...	YES
or	Alternate spelling for ||
Group 15 (right-to-left associativity)
? :	Ternary conditional (if-then-else)	int i = (a > b) ? a : b;	NO
Group 16 (right-to-left associativity)
=	Assignment operator	int a = b;	YES
+=	Increment and assign	a += 3;	YES
-=	Decrement and assign	b -= 4;	YES
*=	Multiply and assign	a *= 5;	YES
/=	Divide and assign	a /= 2;	YES
%=	Modulo and assign	a %= 3;	YES
&=	Bitwise AND and assign	flags &= new_flags;	YES
and_eq	Alternate spelling for &=
^=	Bitwise exclusive or (XOR) and assign	flags ^= new_flags;	YES
xor_eq	Alternate spelling for ^=
|=	Bitwise normal OR and assign	flags |= new_flags;	YES
or_eq	Alternate spelling for |=
<<=	Bitwise shift left and assign	flags <<= 2;	YES
>>=	Bitwise shift right and assign	flags >>= 2;	YES
Group 17
throw	throw exception	throw EClass(“Message”);	NO
Group 18
,	Sequential evaluation operator	for( i = 0, j = 0; i < 10; i++, j++ ) …	YES