3.5 Bytes and Byte Strings

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▼ | 3 | Built-In Datatypes

3.1 | Booleans
3.2 | Numbers
3.3 | Characters
3.4 | Strings (Unicode)
3.5 | Bytes and Byte Strings
3.6 | Symbols
3.7 | Keywords
3.8 | Pairs and Lists
3.9 | Vectors
3.10 | Hash Tables
3.11 | Boxes
3.12 | Void and Undefined

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#### 3.5`` Bytes and Byte Strings

A byte is an exact integer between 0 and 255, inclusive. The byte? predicate recognizes numbers that represent bytes.

Examples:
> ( byte? 0)
#t
> ( byte? 256)
#f

A byte string is similar to a string – see Strings (Unicode) – 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.

> > > Reading Strings in Reference: Racket documents the fine points of the syntax of byte strings.

Examples:
> #"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 Input and Output). 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:
> ( display #"Apple")
Apple
> ( display "\316\273") ; same as "Î»"
Î»
> ( 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:
> ( bytes->string/utf-8 #"\316\273")
"λ"
> ( bytes->string/latin-1 #"\316\273")
"Î»"

> ( 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: #"\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"

> > > Byte Strings in Reference: Racket provides more on byte strings and byte-string procedures.

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