~的优先级与>>的优先级问题

hahali 2011-08-21 08:38:37



#include <iostream>

using namespace std;



int main(void)

{

	unsigned char a = 0xA5;

	unsigned char b = ~a>>4;

	printf("%d\n", b);

	return 0;

}

求b的值。

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hahali 2011-11-15

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[Quote=引用 5 楼 jake443403168 的回复:]
帮你查了一下书，~优先级高于>>
[/Quote]
这个我知道，只有结果不是那样的才发帖求助的！

hahali 2011-11-15

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[Quote=引用 1 楼 lthyxy 的回复:]
我又不是你的是电脑
[/Quote]
不知道答案不要回帖

赵4老师 2011-08-22

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记不住就加括号。
Operator Precedence and Associativity
The table below lists the C and C++ operators and their precedence and associativity values. The highest precedence level is at the top of the table.

Symbol Name or Meaning Associativity
Highest Precedence
++ Post-increment Left to right
-- Post-decrement
( ) Function call
[ ] Array element
-> Pointer to structure member
. Structure or union member
++ Pre-increment Right to left
-- Pre-decrement
! Logical NOT
~ Bitwise NOT
- Unary minus
+ Unary plus
& Address
* Indirection
sizeof Size in bytes
new Allocate program memory
delete Deallocate program memory
(type) Type cast [for example, (float) i]
.* Pointer to member (objects) Left to right
->* Pointer to member (pointers)
* Multiply Left to right
/ Divide
% Remainder
+ Add Left to right
- Subtract
<< Left shift Left to right
>> Right shift
< Less than Left to right
<= Less than or equal to
> Greater than
>= Greater than or equal to
== Equal Left to right
!= Not equal
& Bitwise AND Left to right
^ Bitwise exclusive OR Left to right
| Bitwise OR Left to right
&& Logical AND Left to right
|| Logical OR Left to right
? : Conditional Right to left
= Assignment Right to left
*=, /=, %=, +=, -=, <<=, >>=, &=, ^=, |= Compound assignment
, Comma Left to right
Lowest Precedence

we_sky2008 2011-08-22

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[Quote=引用 12 楼 we_sky2008 的回复:]
楼主，这个不是优先级的问题，是整值提升的原因
小于整型的数据类型在参加计算之前会首先提升为int类型，

C/C++ code

unsigned char a = 0xA5;//32位下，a在参加下面的~a之前会先整值提升为0x000000A5;
unsigned char b = ~a>>4;//所以~a == 0xFFFFFFA5，当右移是逻辑移位时，~a >……
[/Quote]
修改下，刚才取反时值搞错了，应该是：



升为0x000000A5;

    unsigned char b = ~a>>4;//所以~a == 0xFFFFFF5A，当右移是逻辑移位时，~a >> 4 == 0x0FFFFFF5;，当右移是算术移位时，，~a >> 4 == 0xFFFFFFF5；当赋值时发生截断之后，b的值都是0xF5

sunnyorange 2011-08-22

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[Quote=引用 12 楼 we_sky2008 的回复:]

楼主，这个不是优先级的问题，是整值提升的原因
小于整型的数据类型在参加计算之前会首先提升为int类型，
C/C++ code

unsigned char a = 0xA5;//32位下，a在参加下面的~a之前会先整值提升为0x000000A5;
unsigned char b = ~a>>4;//所以~a == 0xFFFFFFA5，当右移是逻辑移位时，~a >> 4 =……
[/Quote]

学习了~~

we_sky2008 2011-08-22

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楼主，这个不是优先级的问题，是整值提升的原因
小于整型的数据类型在参加计算之前会首先提升为int类型，



    unsigned char a = 0xA5;//32位下，a在参加下面的~a之前会先整值提升为0x000000A5;

    unsigned char b = ~a>>4;//所以~a == 0xFFFFFFA5，当右移是逻辑移位时，~a >> 4 == 0x0FFFFFFA;，当右移是算术移位时，，~a >> 4 == 0xFFFFFFFA；当赋值时发生截断之后，b的值都是0xFA

hahali 2011-08-22