The application of the C-language bit segment: The number of bits in the statistics binary

A bit segment is a special struct that is used less in the C language, and the C language allows you to specify the memory length of its members in bits in a struct, which is called a bit field or bit field in bits. Use bit segments to store data with fewer digits.

the access to information is generally measured in bytes. In fact, sometimes storing a message does not have to use one or more bytes, for example, "true" or "false" with 0 or 1, just 1 bits. When the computer is used in the field of Process control, parameter detection or data communication, control information often occupies only one or several bits in one byte, often putting a few information in one byte. How to assign and change the value of one or several bits in a byte? There are two ways to do this:(1) An integer variable data can be artificially divided into several parts. but it's too cumbersome to assign a certain number of bits in a byte in this way. A method that can segment the structure body.

struct packed-data{          unsigned a:2;          unsigned b:6;          unsigned c:4;          unsigned d:4;          int i;} Data

The structure of its memory allocation is as follows

The statistical information of the data can be realized by using the bit segment structure.

Reference title: Number of 1

Topic analysis, the subject is clearly asked to count the number of input integers 1, of course, the problem can also use bit operations to statistics, here, we use a bit segment for the knot.

It is known that the input data n<=1000<2^16, so the design of 16-bit structural posture segment

typedef struct A{UNSIGNED Short a0:1, unsigned short a1:1, unsigned short a2:1, unsigned short a3:1, unsigned short a4:1;< c5/>unsigned short a5:1; unsigned short a6:1; unsigned short a7:1; unsigned short a8:1; unsigned short a9:1; unsigned short a10:1; unsigned short a11:1; unsigned short a12:1; unsigned short a13:1; unsigned short a14:1; unsigned short a15:1; }datatype;

take a name for each bit AI 0<=i<16

Then, to find a way to convert the whole number into a paragraph, the direct assignment is definitely wrong, using each bit assignment, requires in-place operation, complex and error-prone, here, we want to use a memory copy function memcpy (void*,void*,size_t)

In fact, whether it is a struct, an array, or an int variable, in the final analysis or continuous representation in memory, the memcpy function can achieve a copy of the data, based on the memory level.

Reference Source:

#include <memory.h> #include <iostream>using namespace std; #define  sums (b) b.a0+b.a1+b.a2+b.a3+b.a4+ b.a5+b.a6+b.a7+b.a8+b.a9+b.a10+b.a11+b.a12+b.a13+b.a14+b.a15typedef struct a{unsigned short a0:1, unsigned short a1:1 ; unsigned short a2:1; unsigned short a3:1; unsigned short a4:1;  unsigned short a5:1; unsigned short a6:1; unsigned short a7:1; unsigned short a8:1; unsigned short a9:1; unsigned short a10:1; unsigned short a11:1; unsigned short a12:1; unsigned short a13:1; unsigned short a14:1; unsigned short a15:1; }datatype;int Main (int argc, char** argv) {DATATYPE p;int c;int n;//scanf ("%d", &n); Cin>>n;while (n) {unsigned Short b;n--;cin>>b;memcpy (&p,&b,sizeof); C=sums (P); Cout<<c<<endl;} return 0;}

The application of the C-language bit segment: The number of bits in the statistics binary