字节顺序
Endianness is the storage rule for program objects that cross multiple bytes, and represents the arrangement method of the bytes of an object.
There are two endianness: little endian and big endian.
In fact, there is no difference between these two endianness. The names of these two sequences (little endian and big endian) are exactly taken from the book Gulliver's Travels. The reason for which the two factions can't stop fighting in the book is that they cannot agree on which end to break shell of the egg. And similar to the egg problem, the choice of endianness has become an argument unrelated to technical reasons.
Of course, the inconsistency of the endianness will cause the binary data to be reversed when transmitting between different types of machines. To avoid this, the network application has established a set of standards to ensure that the agreed network standard is used during the transmitting process, rather than the internal representation of different machines.
Below, we take a variable located at 0x100 with type int and hexadecimal value 0x01234567 as an example to introduce two endianness:
Here 0x01 is the most significant byte, and 0x67 is the least significant byte.
Little endian¶
Little endian means that the machine chooses to store objects in the memory in the order from the lowest effective byte to the highest effective byte.
The variables mentioned above are expressed as follows:
| .... | 0x100 | 0x101 | 0x102 | 0x103 | .... |
|---|---|---|---|---|---|
| .... | 67 | 45 | 23 | 01 | .... |
Big endian¶
Big endian means that the machine chooses to store objects in the memory in the order from the highest effective byte to the lowest effective byte.
The variables mentioned above are expressed as follows:
| .... | 0x100 | 0x101 | 0x102 | 0x103 | .... |
|---|---|---|---|---|---|
| .... | 01 | 23 | 45 | 67 | .... |
Convention¶
Little endian: x86, ARM processors running Android, iOS, and Windows.
Big endian: Sun, PPC Mac, Internet.
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