如何读取ASCII值在128-130范围内并将其转换为int值的char

Question

I have an array of chars, some of them are ASCII 128 and 130 in decimal. I am trying to read them as normal chars, but instead of 128 I get 8218 as an int (casted to byte, got 26). I need to get that number between 128 and 130. I found some articles on Encodings, some people say I need to use Encoding 439.

Any ideas?

Answer 1

A char (System.Char) in the CLR environment is an unsigned 16-bit number, a UTF-16 code unit . From the Unicode Standard, Chapter 3, §3.9 :

Code unit: The minimal bit combination that can represent a unit of encoded text for processing or interchange.

• Code units are particular units of computer storage. Other character encoding standards typically use code units defined as 8-bit units—that is, octets. The Unicode Standard uses 8-bit code units in the UTF-8 encoding form, 16-bit code units in the UTF-16 encoding form, and 32-bit code units in the UTF-32 encoding form.

• A code unit is also referred to as a code value in the information industry.

• In the Unicode Standard, specific values of some code units cannot be used to represent an encoded character in isolation. This restriction applies to isolated surrogate code units in UTF-16 and to the bytes 80–FF in UTF-8. Similar restrictions apply for the implementations of other character encoding standards; for example, the bytes 81–9F, E0–FC in SJIS (Shift-JIS) cannot represent an encoded character by themselves.

Your "ASCII" text is no longer ASCII once it's in the CLR world. ASCII is a 7-bit encoding and the code points 0x00–0x7F are maintained across all Unicode encodings (UTF-8, -16, -24, -32) for the sake of compatability. In the non-Unicode world, 0x80–0xFF have always had multiple character mappings (and don't even look at EBCDIC vs ASCII). Some ASCII implementations provided for parity as well: the high order bit would be set to maintain the desired parity.

• Even parity. The high order bit is set to maintain an even number of 'on' bits in the octet.
• Odd parity. The high order bit is set to maintain an odd number of 'on' bits in the octet.
• No parity. The high order bit is never set.

Presumably you're reading your "ASCII" text using a UTF-8 encoder/decoder (the CLR default). To get the numeric values you expect in your chars, you'll need to read the text using an encode/decoder suitable for the encoding your text is actually in (Windows 1252? something else?).

A better approach for you, perhaps, would be to read your text octet by octet as binary, using System.IO.FileStream , rather than System.IO.TextReader and its minions. Then you've got the raw octets and you can convert them to text as you wish, or do math on the raw octet values.