Does Linux C language have bits?

Linux C language has bit; in the microcontroller C language, bit is a new keyword, often used to define a "bit variable"; the method of defining bit type data in C language is: 1. Through sbit Or bit definition; 2. Define through bit field (in structure); 3. Define through combined bit operators.

#The operating environment of this tutorial: linux5.9.8 system, Dell G3 computer.

Does Linux C language have bits?

have.

C language defines bit type data:

1. Definition through sbit or bit

sbit is mapped to the IO port (IO such as P1^1 The "bit" of the port)

bit is in the bit-addressable space in RAM and is generally used as a flag bit for program judgment.

Consider that one of them is external (sbit) and the other is internal (bit).

In the microcontroller C language, bit is a new keyword, often used to define a "bit variable"

2. Define through bit fields (in structures)

Definition of bit fields and description of bit field variables Bit field definition is similar to structure definition, and its form is:

　struct bit field structure name

　{Bit field list};

The form of the bit field list is: Type specifier bit domain name: bit field length

For example:

struct bs 
{ 
　int a:8; 
　int b:2; 
　int c:6; 
};

The description of bit field variables is the same as the description of structure variables. You can define first and then explain, define and explain at the same time, or explain directly. For example:

struct bs 
{ 
　int a:8; 
　int b:2; 
　int c:6; 
}data;

It indicates that data is a bs variable, occupying two bytes in total. Bit field a occupies 8 bits, bit field b occupies 2 bits, and bit field c occupies 6 bits. There are several explanations for the definition of bit fields:

1. A bit field must be stored in the same byte and cannot span two bytes. If the remaining space of one byte is not enough to store another bit field, the bit field should be stored from the next unit. You can also intentionally start a bit field from the next unit. For example:

struct bs 
{ 
　unsigned a:4 
　unsigned :0 /*空域*/ 
　unsigned b:4 /*从下一单元开始存放*/ 
　unsigned c:4 
}

In this bit field definition, a occupies 4 bits of the first byte, fill in the last 4 bits with 0 to indicate not used, b starts from the second byte, occupying 4 bits, and c occupies 4 bits Bit.

　2. Since the bit field is not allowed to span two bytes, the length of the bit field cannot be greater than the length of one byte, that is, it cannot exceed 8 binary bits.

　3. The bit field can have no bit domain name. At this time, it is only used for filling or adjusting the position. Unnamed bit fields cannot be used. For example:

struct k 
{ 
　int a:1 
　int :2 /*该2位不能使用*/ 
　int b:3 
　int c:2 
};

From the above analysis, it can be seen that bit field is essentially a structure type, but its members are allocated in binary terms.

2. The use of bit fields

The use of bit fields is the same as the use of structure members. Its general form is: Bit field variable name • Bit domain name Bit fields allow output in various formats.

main(){ 
　struct bs 
　{ 
　　unsigned a:1; 
　　unsigned b:3; 
　　unsigned c:4; 
　} bit,*PBit; 
　bit.a=1; 
　bit.b=7; 
　bit.c=15; 
　printf("%d,%d,%d\n",bit.a,bit.b,bit.c); 
　PBit=&bit; 
　PBit->a=0; 
　PBit->b&=3; 
　PBit->c|=1; 
　printf("%d,%d,%d\n",PBit->a,PBit->b,PBit->c); 
}

The above example program defines the bit field structure bs, and the three bit fields are a, b, and c. The variable bit of type bs and the pointer variable PBit pointing to type bs are explained. This means that bitfields can also use pointers.

Lines 9, 10, and 11 of the program assign values ​​to three bit fields respectively. (It should be noted that the assignment cannot exceed the allowable range of the bit field) Line 12 of the program outputs the contents of the three fields in integer format. Line 13 sends the address of the bit field variable bit to the pointer variable PBit. Line 14 uses a pointer to reassign bit field a to 0. Line 15 uses the compound bit operator "&=". This line is equivalent to: PBit->b=PBit->b&3. The original value in bit field b is 7, and the result of the bitwise AND operation with 3 is 3 (111&011=011, decimal value is 3). Similarly, the compound bit operation "|=" is used in line 16 of the program, which is equivalent to: PBit->c=PBit->c|1 and the result is 15. Line 17 of the program outputs the values ​​of these three fields using pointers.

The main purpose of using bit fields is to compress storage. The general rules are:

1) If the types of adjacent bit fields are the same and the sum of their bit widths is less than the sizeof size of the type , then the following field will be stored immediately next to the previous field until it cannot be accommodated;

2) If the types of adjacent bit field fields are the same, but the sum of their bit widths is greater than the sizeof size of the type, then the following field The field will start from a new storage unit with an offset that is an integer multiple of its type size;

3) If bitfield fields are interspersed with non-bitfield fields, no compression will be performed;

4) The total size of the entire structure is an integer multiple of the size of the widest basic type member.

3. Operate by combining bit operators

#define Setbit(x,y)  (x|=(0x01<<y))   //置位
#define Clrbit(x,y)  (x&=（~(0x01<<y))）  //复位（清零）
#define Chkbit(x,y)  (x&(0x01<<y))   　　//检位

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