Embedded Programming with Modern C++ Cookbook

Endianness

Endianness defines the order in which bytes that represent large numerical values are stored in memory.

There are two types of endianness:

• Big-endian: The most significant byte is stored first. The 0x01020304 32-bit value is stored at the ptr address as follows:

  Offset in memory	Value
  ptr	0x01
  ptr + 1	0x02
  ptr + 2	0x03
  ptr + 3	0x04

Examples of big-endian architectures are AVR32 and Motorola 68000.

• Little-endian: The least significant byte is stored first. The 0x01020304 32-bit value is stored at the ptr address as follows:

  Offset in memory	Value
  ptr	0x04
  ptr + 1	0x03
  ptr + 2	0x02
  ptr + 3	0x01

The x86 architecture is little-endian.

• Bi-endian: Hardware supports switchable endianness. Some examples ...