info guile

6.6.5.5 String Selection

Portions of strings can be extracted by these procedures. string-ref delivers individual characters whereas substring can be used to extract substrings from longer strings.

Scheme Procedure: string-length string
C Function: scm_string_length (string): Return the number of characters in string.

C Function: size_t scm_c_string_length (SCM str): Return the number of characters in str as a size_t.

Scheme Procedure: string-ref str k
C Function: scm_string_ref (str, k): Return character k of str using zero-origin indexing. k must be a valid index of str.

C Function: SCM scm_c_string_ref (SCM str, size_t k): Return character k of str using zero-origin indexing. k must be a valid index of str.

Scheme Procedure: string-copy str [start [end]]

C Function: scm_substring_copy (str, start, end)

C Function: scm_string_copy (str)

Return a copy of the given string str.

The returned string shares storage with str initially, but it is copied as soon as one of the two strings is modified.

Scheme Procedure: substring str start [end]

C Function: scm_substring (str, start, end)

Return a new string formed from the characters of str beginning with index start (inclusive) and ending with index end (exclusive). str must be a string, start and end must be exact integers satisfying:

0 <= start <= end <= (string-length str).

The returned string shares storage with str initially, but it is copied as soon as one of the two strings is modified.

Scheme Procedure: substring/shared str start [end]
C Function: scm_substring_shared (str, start, end): Like substring, but the strings continue to share their storage even if they are modified. Thus, modifications to str show up in the new string, and vice versa.

Scheme Procedure: substring/copy str start [end]
C Function: scm_substring_copy (str, start, end): Like substring, but the storage for the new string is copied immediately.

Scheme Procedure: substring/read-only str start [end]
C Function: scm_substring_read_only (str, start, end): Like substring, but the resulting string can not be modified.

C Function: SCM scm_c_substring (SCM str, size_t start, size_t end)
C Function: SCM scm_c_substring_shared (SCM str, size_t start, size_t end)
C Function: SCM scm_c_substring_copy (SCM str, size_t start, size_t end)
C Function: SCM scm_c_substring_read_only (SCM str, size_t start, size_t end): Like scm_substring, etc. but the bounds are given as a size_t.

Scheme Procedure: string-take s n
C Function: scm_string_take (s, n): Return the n first characters of s.

Scheme Procedure: string-drop s n
C Function: scm_string_drop (s, n): Return all but the first n characters of s.

Scheme Procedure: string-take-right s n
C Function: scm_string_take_right (s, n): Return the n last characters of s.

Scheme Procedure: string-drop-right s n
C Function: scm_string_drop_right (s, n): Return all but the last n characters of s.

Scheme Procedure: string-pad s len [chr [start [end]]]

Scheme Procedure: string-pad-right s len [chr [start [end]]]

C Function: scm_string_pad (s, len, chr, start, end)

C Function: scm_string_pad_right (s, len, chr, start, end)

Take characters start to end from the string s and either pad with chr or truncate them to give len characters.

string-pad pads or truncates on the left, so for example

(string-pad "x" 3)     ⇒ "  x"
(string-pad "abcde" 3) ⇒ "cde"

string-pad-right pads or truncates on the right, so for example

(string-pad-right "x" 3)     ⇒ "x  "
(string-pad-right "abcde" 3) ⇒ "abc"

Scheme Procedure: string-trim s [char_pred [start [end]]]

Scheme Procedure: string-trim-right s [char_pred [start [end]]]

Scheme Procedure: string-trim-both s [char_pred [start [end]]]

C Function: scm_string_trim (s, char_pred, start, end)

C Function: scm_string_trim_right (s, char_pred, start, end)

C Function: scm_string_trim_both (s, char_pred, start, end)

Trim occurrences of char_pred from the ends of s.

string-trim trims char_pred characters from the left (start) of the string, string-trim-right trims them from the right (end) of the string, string-trim-both trims from both ends.

char_pred can be a character, a character set, or a predicate procedure to call on each character. If char_pred is not given the default is whitespace as per char-set:whitespace (see section Standard Character Sets).

(string-trim " x ")              ⇒ "x "
(string-trim-right "banana" #\a) ⇒ "banan"
(string-trim-both ".,xy:;" char-set:punctuation)
                  ⇒ "xy"
(string-trim-both "xyzzy" (lambda (c)
                             (or (eqv? c #\x)
                                 (eqv? c #\y))))
                  ⇒ "zz"

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