Fundamentals of Computer Science I: Media Computing (CS151.01 2008S)

Reference: String Procedures


String Predicates

(string? val)
Standard String Predicate. Determine if val is a string.

String Constructors

(make-string length ch)
Standard String Procedure. Create a new string of length length, containing only copies of ch.
(string ch_0 ch_1 ... ch_n)
Standard String Procedure. Create a new string of length n+1, by concatenating all of ch_0 through ch_n.
(string-append str_0 str_1 ... str_n)
Standard String Procedure. Create a new string of by joining together str through str_n in order. (Much like append, but for strings, rather than lists.)

Extracting Information from Strings

(string-length str)
Standard String Procedure. Determine the number of characters in str.
(string-ref str pos)
Standard String Procedure. Extract the character at a specified position from a string. Like list-ref, string-ref presupposes zero-based indexing; the position is specified by the number of characters that precede it in the string. Hence, the initial character in the string is at position 0, the next at position 1, and so on.)
(substring str start end)
Standard String Procedure. Create a new string by selecting the characters at positions start to end-1 of str. Note that substring, like string-ref uses 0-based indexing.

Converting Strings

(string->list str)
Standard String Procedure. Convert str to a list of characters. The ith element of the list is the ith character in the string.
(list->string char-list)
Standard String Procedure. Convert char-list (which must be a list of characters) to a string. The ith element of the list becomes the ith character in the string.
(string->number str)
Standard String Procedure. Given a string that naturally represents a number (e.g., "23" or "3.14", or even "2.11e-5"), return the corresponding number.
(number->string num)
Standard String Procedure. Convert num to an appropriate textual representation.

Comparing Strings

(string<? str1 str2)
Standard String Procedure. Determine whether str1 lexicographically precedes str2. Both str1 and str2 must be strings.
(string<=? str1 str2)
Standard String Procedure. Holds if str1 is either the same as str2 or if str1 lexicographically precedes str2. Both str1 and str2 must be strings.
(string=? str1 str2)
Standard String Procedure. Holds if str1 is the same as str2. Both str1 and str2 must be strings.
(string>=? str1 str2)
Standard String Procedure. Holds if str1 is either the same as str2 or if str1 lexicographically follows str2. Both str1 and str2 must be strings.
(string>? str1 str2)
Standard String Procedure. Determine whether str1 lexicographically follows str2. Both str1 and str2 must be strings.
(string-ci<? str1 str2)
Standard String Procedure. Determine whether str1 lexicographically precedes str2, ignoring case. Both str1 and str2 must be strings.
(string-ci<=? str1 str2)
Standard String Procedure. Holds if str1 is either the same as str2 or if str1 lexicographically precedes str2, ignoring case. Both str1 and str2 must be strings.
(string-ci=? str1 str2)
Standard String Procedure. Holds if str1 is the same as str2, ignoring case. Both str1 and str2 must be strings.
(string-ci>=? str1 str2)
Standard String Procedure. Holds if str1 is either the same as str2 or if str1 lexicographically follows str2, ignoring case. Both str1 and str2 must be strings.
(string-ci>? str1 str2)
Standard String Procedure. Determine whether str1 lexicographically follows str2, ignoring case. Both str1 and str2 must be strings.

Creative Commons License

Samuel A. Rebelsky, rebelsky@grinnell.edu

Copyright (c) 2007-8 Janet Davis, Matthew Kluber, and Samuel A. Rebelsky. (Selected materials copyright by John David Stone and Henry Walker and used by permission.)

This material is based upon work partially supported by the National Science Foundation under Grant No. CCLI-0633090. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

This work is licensed under a Creative Commons Attribution-NonCommercial 2.5 License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc/2.5/ or send a letter to Creative Commons, 543 Howard Street, 5th Floor, San Francisco, California, 94105, USA.