Moxa DA-662A-16-LX [50/63] Be careful when developing migrating programs

DA-662A Series Software Programmer's Guide

The difference between Big endian and Little endian

Big-endian and little-endian describe the order in which a sequence of bytes are stored in computer memory.

For big-endian, the ―big end‖ (most significant value in the sequence) is stored first (i.e., at the lowest storage

address). For little-endian, the ―little end‖ (least significant value in the sequence) is stored first. For example,

in a big-endian computer, the two bytes required for the hex number 1234 would be stored as 1234 in storage

2. If you will be transmitting 2 or more bytes of data at the same time (e.g., short, int, or long data types) you

must pay special attention to the Endian nature of the data convert if necessary.

Useful APIs for converting Big endian and Little endian

htonl(): Converts the unsigned integer hostlong from host byte order to network byte order.

htons(): Converts the unsigned short integer hostshort from host byte order to network byte order.

ntohl(): Converts the unsigned integer netlong from network byte order to host byte order.

ntohs(): Converts the unsigned short integer netshort from network byte order to host byte order.

Conversion Example

If a big endian computer wants to transfer data to a little endian computer, the structure of the data format is:

struct data_struct {

Assume int a=0x12345678. When the data is transferred from computer A to computer B, the content of int a

will be 0x78563412 if you do not do any conversions. Under the status, you can utilize ntohl(a) to convert

variable a to get the correct information.