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1. Concepts

The so-called large-end and small-end refers to the byte sequence of Multi-byte data types (such as INT) stored in the memory. The small end means that the low address bytes store the low data level, and the high address bytes store the high data level. The Large End refers to the high data level and the high data level in the low address bytes. To put it simply, the high level of data stored in low bytes is the big end, and the low level is the small end.

The following is an example to illustrate the different storage sequence of the integer 0x12345678 in large-end and small-end mode.

 

Memory Address	Small-end Mode	Big end Mode
Zero X 5250	0x78	0x12
Zero X 5251	0x56	0x34
Zero X 5252	0x34	0x56
Zero X 5253	0x12	0x78

 

You may wonder if I made a mistake. But it is true, because 12 is a high data level, and 78 is a low data level.

2. How to judge

The basic principle of determination is to extract the first byte of a Multi-byte data structure. If the byte is a high data level, the machine is a large end. If the byte is a low data level, then the machine is a small terminal. Do not talk nonsense, on the code.

2.1 pointer Conversion

# Nclude <stdio. h> int isbigendian (); int main () {printf ("size of int type: % d bytes. \ n ", sizeof (INT); int endianflag = isbigendian (); printf (" endianflag: % d \ n ", endianflag); If (endianflag) {printf ("this is a big endian machine. \ n ");} else {printf (" This Is Not A Big endian machine. \ n ") ;}return 0 ;}int isbigendian () {int A = 0x12345678; // convert the int forced type to Char single-byte char B = * (char *) & A; // determine the initial storage location, that is, the content of the first byte, if (B = 0x78) {return 0;} return 1 ;}

2.2 Union

#include <stdio.h>int isBigEndian();int main(){printf("Size of int type:%d bytes.\n",sizeof(int));int endianFlag=isBigEndian();printf("endianFlag:%d\n",endianFlag);if (endianFlag){printf("This is a Big Endian machine.\n");}else{printf("This is NOT a Big Endian machine.\n");}return 0;}int isBigEndian()  {union IntCharUnion{  int a;char b;}temp; temp.a = 0x12345678;  if(temp.b == 0x78){return 0;}return 1;}

 

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