Byte order: big endian vs little endian

How to quickly remember

big-endian also called Large tail sequence , The tail of the value is stored in the large address . The tail is relative to the variable value we know , Large means address ;
Corresponding ,little-endian also called Little endings , The tail of the value is stored in a small address .
In a word, size is the address of the tail , The tail is the tail of numbers , refer to 0xABCD( Decimal system 43981) Of D

How to determine whether the byte order is large or small

1. View through binary tools : readelf -h main

int main(){
    
	return 0;
}

Compile binary

g++ main.cpp -o main

Use readelf Check byte order

readelf -h main

give the result as follows (ELF Magic The first 6 Bytes represent byte order ,0 Invalid format ; 1 Small end format ; 2 Big end format )
ELF Header:
Magic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
Class: ELF64
Data: 2’s complement, little endian
Version: 1 (current)
OS/ABI: UNIX - System V
ABI Version: 0
Type: DYN (Shared object file)
Machine: Advanced Micro Devices X86-64
Version: 0x1
Entry point address: 0x1060
Start of program headers: 64 (bytes into file)
Start of section headers: 14976 (bytes into file)
Flags: 0x0
Size of this header: 64 (bytes)
Size of program headers: 56 (bytes)
Number of program headers: 14
Size of section headers: 64 (bytes)
Number of section headers: 32
Section header string table index: 31

2. Use the command line to view : lscpu | grep -i byte

[email protected]:~/ws/thread_local$ lscpu | grep -i byte
Byte Order: Little Endian

3. Use the code (union) Judge

 #include <stdio.h>
 
 union Endian {
    
     char a;
     int b;
 };
 
 int main(){
    
     Endian endian;
     endian.b = 1;
 
     if (endian.a == 1) {
    
         printf("little endian\n");
     }else{
    
         printf("big endian\n");
     }   
     return 0;
 }

[email protected]:~/ws$ ./main
little endian

Network order

Network transmission generally adopts large end sequence , Also known as network byte order , Or network sequence .IP The protocol defines the large end order as the network byte order .