3.4 Strings (Unicode)
A string is a fixed-length array of characters. It prints using doublequotes, where doublequote and backslash characters within the string are escaped with backslashes. Other common string escapes are supported, including \n for a linefeed, \r for a carriage return, octal escapes using \ followed by up to three octal digits, and hexadecimal escapes with \u (up to four digits). Unprintable characters in a string are normally shown with \u when the string is printed.
Reading Strings in Reference: Racket documents the fine points of the syntax of strings.
The display procedure directly writes the characters of a string to the current output port (see Input and Output), in contrast to the string-constant syntax used to print a string result.
Examples: | ||
| > "Apple" | ||
"Apple" | ||
| > "\u03BB" | ||
"λ" | ||
| > (display "Apple") | ||
Apple | ||
| > (display "a \"quoted\" thing") | ||
a "quoted" thing | ||
| > (display "two\nlines") | ||
| ||
| > (display "\u03BB") | ||
λ |
A string can be mutable or immutable; strings written directly as expressions are immutable, but most other strings are mutable. The make-string procedure creates a mutable string given a length and optional fill character. The string-ref procedure accesses a character from a string (with 0-based indexing); the string-set! procedure changes a character in a mutable string.
Examples: |
| > (string-ref "Apple" 0) |
#\A |
| > (define s (make-string 5 #\.)) |
| > s |
"....." |
| > (string-set! s 2 #\λ) |
| > s |
"..λ.." |
String ordering and case operations are generally locale-independent; that is, they work the same for all users. A few locale-dependent operations are provided that allow the way that strings are case-folded and sorted to depend on the end-user’s locale. If you’re sorting strings, for example, use string<? or string-ci<? if the sort result should be consistent across machines and users, but use string-locale<? or string-locale-ci<? if the sort is purely to order strings for an end user.
Examples: | ||
| > (string<? "apple" "Banana") | ||
#f | ||
| > (string-ci<? "apple" "Banana") | ||
#t | ||
| > (string-upcase "Straße") | ||
"STRASSE" | ||
| ||
"STRAßE" |
For working with plain ASCII, working with raw bytes, or encoding/decoding Unicode strings as bytes, use byte strings.