|
|
|
|
|
# Bytes and Byte Strings
|
|
|
|
|
|
|
|
|
|
|
|
A _byte_ is an exact integer between `0` and `255`, inclusive. The
|
|
|
|
|
|
`byte?` predicate recognizes numbers that represent bytes.
|
|
|
|
|
|
|
|
|
|
|
|
Examples:
|
|
|
|
|
|
|
|
|
|
|
|
```racket
|
|
|
|
|
|
> (byte? 0)
|
|
|
|
|
|
#t
|
|
|
|
|
|
> (byte? 256)
|
|
|
|
|
|
#f
|
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
|
|
A _byte string_ is similar to a string—see \[missing\]—but its content
|
|
|
|
|
|
is a sequence of bytes instead of characters. Byte strings can be used
|
|
|
|
|
|
in applications that process pure ASCII instead of Unicode text. The
|
|
|
|
|
|
printed form of a byte string supports such uses in particular, because
|
|
|
|
|
|
a byte string prints like the ASCII decoding of the byte string, but
|
|
|
|
|
|
prefixed with a `#`. Unprintable ASCII characters or non-ASCII bytes in
|
|
|
|
|
|
the byte string are written with octal notation.
|
|
|
|
|
|
|
|
|
|
|
|
> +\[missing\] in \[missing\] documents the fine points of the syntax of
|
|
|
|
|
|
> byte strings.
|
|
|
|
|
|
|
|
|
|
|
|
Examples:
|
|
|
|
|
|
|
|
|
|
|
|
```racket
|
|
|
|
|
|
> #"Apple"
|
|
|
|
|
|
#"Apple"
|
|
|
|
|
|
> (bytes-ref #"Apple" 0)
|
|
|
|
|
|
65
|
|
|
|
|
|
> (make-bytes 3 65)
|
|
|
|
|
|
#"AAA"
|
|
|
|
|
|
> (define b (make-bytes 2 0))
|
|
|
|
|
|
> b
|
|
|
|
|
|
#"\0\0"
|
|
|
|
|
|
> (bytes-set! b 0 1)
|
|
|
|
|
|
> (bytes-set! b 1 255)
|
|
|
|
|
|
> b
|
|
|
|
|
|
#"\1\377"
|
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
|
|
The `display` form of a byte string writes its raw bytes to the current
|
|
|
|
|
|
output port \(see \[missing\]\). Technically, `display` of a normal
|
|
|
|
|
|
\(i.e,. character\) string prints the UTF-8 encoding of the string to
|
|
|
|
|
|
the current output port, since output is ultimately defined in terms of
|
|
|
|
|
|
bytes; `display` of a byte string, however, writes the raw bytes with no
|
|
|
|
|
|
encoding. Along the same lines, when this documentation shows output, it
|
|
|
|
|
|
technically shows the UTF-8-decoded form of the output.
|
|
|
|
|
|
|
|
|
|
|
|
Examples:
|
|
|
|
|
|
|
|
|
|
|
|
```racket
|
|
|
|
|
|
> (display #"Apple")
|
|
|
|
|
|
Apple
|
|
|
|
|
|
> (display "\316\273") ; same as "λ"
|
|
|
|
|
|
λ
|
|
|
|
|
|
> (display #"\316\273") ; UTF-8 encoding of λ
|
|
|
|
|
|
λ
|
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
|
|
For explicitly converting between strings and byte strings, Racket
|
|
|
|
|
|
supports three kinds of encodings directly: UTF-8, Latin-1, and the
|
|
|
|
|
|
current locale’s encoding. General facilities for byte-to-byte
|
|
|
|
|
|
conversions \(especially to and from UTF-8\) fill the gap to support
|
|
|
|
|
|
arbitrary string encodings.
|
|
|
|
|
|
|
|
|
|
|
|
Examples:
|
|
|
|
|
|
|
|
|
|
|
|
```racket
|
|
|
|
|
|
> (bytes->string/utf-8 #"\316\273")
|
|
|
|
|
|
"λ"
|
|
|
|
|
|
> (bytes->string/latin-1 #"\316\273")
|
|
|
|
|
|
"λ"
|
|
|
|
|
|
> (parameterize ([current-locale "C"]) ; C locale supports ASCII,
|
|
|
|
|
|
(bytes->string/locale #"\316\273")) ; only, so...
|
|
|
|
|
|
bytes->string/locale: byte string is not a valid encoding
|
|
|
|
|
|
for the current locale
|
|
|
|
|
|
byte string: #"\316\273"
|
|
|
|
|
|
> (let ([cvt (bytes-open-converter "cp1253" ; Greek code page
|
|
|
|
|
|
"UTF-8")]
|
|
|
|
|
|
[dest (make-bytes 2)])
|
|
|
|
|
|
(bytes-convert cvt #"\353" 0 1 dest)
|
|
|
|
|
|
(bytes-close-converter cvt)
|
|
|
|
|
|
(bytes->string/utf-8 dest))
|
|
|
|
|
|
"λ"
|
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
|
|
> +\[missing\] in \[missing\] provides more on byte strings and
|
|
|
|
|
|
> byte-string procedures.
|
