Detailed explanation of shift operator and bit operator in C language

Catalog

1、 Shift operator

2、 Bit operators

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1、 Shift operator

It is divided into the shift left operator （<<） And the shift right operator (>>).

Shift left operator ：

Shift rules ： Abandon on the left , The right to repair 0.

What does that mean , Now let me explain it in detail .

For example, we define an integer variable a, Give it an initial value 5. Such as int a=5; And then a Move left , namely a<<2, What is the result ？ Before we talk about it , We first need to understand integer types 5 How is it stored in memory , If you don't know, please read my previous blog The integer 3 Expression and storage in memory La , There are detailed explanations . integer 5 It is stored in the form of complement . And will be 5 Move left 2 Bit is to move the binary bits stored in memory to the left 2 Bit and put this 2 Bit discard , Right side use 0 A filling . The last thing I got was 5<<2 The result after , The following figure can be used to briefly describe ~

  According to the picture above a<<2 The result is 20.

Shift right operator ：

First, the right shift operation is divided into two types . Arithmetic shift and logical shift .

Arithmetic shift rule ： The left side is filled with the sign bit of the value , On the right side of the discarded .

Logical shift rules ： Use... On the left 0 Add , On the right side of the discarded .

What do you mean by that , Let's take a look at a few examples , Such as the 5 Shift right , namely 5>>1, How much do you get ？

If it is an arithmetic shift , Will be 5 The bits stored in memory move to the right 1 And throw this one away , On the left, the sign bits of the binary bits stored with this value are complemented . Here's the picture ：

therefore 5>>1 The result is 2. What about logical shift , A logical shift is a left-hand shift 0, Add , Right abandon . For positive numbers , Its sign bit is 0, So the result of arithmetic shift is the same as that of logical shift , Logical shift can also be represented by the figure above , The result is also 2.

If the -5 One bit to the right , What is the result . Let's first look at arithmetic shifts , I won't go into details , Please look at the chart below. ：

therefore -5>>1 The result of the arithmetic shift is -3.

Empathy , Let's see -5>>1 What is the result of logical shift ~

Because the highest position is 0, So the end result is 3 La ~. But in general, we use the arithmetic shift .

2、 Bit operators

&      Bitwise （ Binary digit ） And

|      Bitwise （ Binary digit ） or

^      Bitwise （ Binary digit ） Exclusive or

Let's look at this code directly , You can first guess which three numbers are finally output ：

int main()
{
	int a = 3;
	int b = -5;
	printf("%d %d %d", a & b, a | b, a ^ b);
	return 0;
}

Let's analyze first ： Bitwise AND Is to compare the binary bits stored in two numbers , Both are 1 Only then 1, Otherwise 0. therefore a&b Analysis by graph is ：

therefore a&b The result is 3 了 .

Press bit or Namely   Compare the binary bits stored in two numbers , One of the two is 1 for 1, Otherwise 0. therefore a|b Analysis by graph is ：

therefore a|b The value is -5 了 .

Bitwise XOR Namely   Compare the binary bits stored in two numbers , The two are the same 0, Dissimilarity is 1, therefore a^b Analysis by graph is ：

  therefore a^b The result is that -8 La .

Finally, let's let the program run ：

  It is the same as the analysis ~~~

It's over here , I hope you can give me a compliment ~~~