c++ - 位运算符中不明白的地方

Question

对于形如value = value | 1 << bit_number的表达式，目的是将指定位设为1。

不明白的是：此表达式运算符优先级|大于<<吗，要是这样的话，例如：value为01011100，bit_number为3，可是计算之后很多位发生了变化，感觉不太对。那要是<<优先级大于|，那么先将bit_number左移一位，再进行或操作，感觉也是好多为发生了变化。所以，关键点是指定位指的是哪几个位？

先谢谢了。

Answer 1

First of all, << has a higher priority than |.

Secondly, there is a mistake in your understanding: <<The right shift operator shifts the parameter on the left side of the operation to the right by the parameter position on the right side. In other words, 1 << bit_number does not shift bit_number to the right 1 bit, but shift 1 to the right by bit_number bit.
Give your example, when bit_number is 3, the result of 1 << bit_number is 00001000. Then do the AND operation with value of 01011100, and you can change the 4 position from the right to 1.

The designated position is a certain digit, which refers to the bit_number+1th digit

from right to left.

Answer 2

http://jb51.net/article/37282.htm
Priority

Answer 3

<< has a higher priority than |. After the operation, only one bit of value will change at most.

The function of this expression is to set the valueth of bit_number to 1.

For example: value = 01010100, bit_number = 3, the result of the operation is (01010100 | 1000) = 01011100

Answer 4

1 << The bit_number is 0000 0001 (assumed to be 8 bits) and the bit_number bit is shifted to the left, rather than the bit_number is shifted to the left by one bit. If you are not familiar with the basic concept, let’s take a look at the basics first. . . .

Answer 5

1. << has a higher priority than |.

2. 1 << bit_number shifts 1 to the left by bit_number bits, so the result is a binary number containing only one 1 (its bit_number bit from right to left is 1). For example, 1 << 3 gets The binary number is 1000.

3. will be used for bitwise AND operation with value in the future, and the effect should be clear at a glance.