Octet String是什么意思？ Octet和Char有什么区别？

Question

What is the difference between octet string and char? How can an octet string be used? Can anybody write a small C program on Octet string? How are octet strings stored in memory?

Answer 1

Standards (and such) use "octet" to explicitly state that they're talking about 8-bit groups. While most current computers work with bytes that are also 8 bits in size, that's not necessarily the case. In fact, "byte" is rather poorly defined, with considerable disagreement over what it means for sure -- so it's generally avoided when precision is needed.

Nonetheless, on a typical computer, an octet is going to be the same thing as a byte, and an octet stream will be stored in a series of bytes.

Answer 2

• An octet is another word for a 8-bit byte.
• A char is usually 8 bits, but may be another size on some architectures.

Answer 3

An octet is 8 bits meant to be handled together (hence the "oct" in "octet"). It's what we think of when we say "byte" these days.

A char is basically a byte -- it's defined as the smallest addressable unit of memory, which on almost all modern computers is the same as an octet. But there have been computers with 9-bit, 16-bit, even 36-bit "words" that qualify as chars by that definition. You only need to care about those computers (and thus, about the difference between a char and an octet) if you have one -- let the people who have the weird hardware worry about how to make their programs run on it.

Answer 4

An octet string is simply a sequence of bits grouped into chunks of 8. Those 8-sized groups often represent characters. Octet string is a basic data type used for SNMP.

Answer 5

A string used to be a set of octets, which is turn is a set of 8 bits.

A string in C, is always a null-terminated, memory contiguous, set of bytes. Back in the day, each byte, an octet, represented a character. That's why they named the type used to make strings, char .

The ASCII table, that goes from 0 to 127, with the graphics/accents version going from 0 to 255, was no longer enough for displaying characters in a string, so someone though of adding bits to a character representation. Dumb-asses from CS though of 9bit and so forth, to what HW guys replied "are you nuts??? keep it a multiple of memory addressing unit", which was the byte, back then. Enter wide-character strings, ie 16bits per character. On a WC string, each character is represented by 2 bytes... there goes your char=1 byte rule down the drain.

To keep an exact description of a string, if it's a set of characters-represented-by-8bits (in Earth, following the ASCII table, but I've been to Mars), it's an "octet string".

If it's not "octet string" it may or may not be WC... Joel was a nice post on this.