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13.3.3 Strings

Strings in CMUCL are UTF-16 strings. That is, for Unicode code points greater than 65535, surrogate pairs are used. We refer the reader to the Unicode standard for more information about surrogate pairs. We just want to make a note that because of the UTF-16 encoding of strings, there is a distinction between Lisp characters and Unicode codepoints. The standard string operations know about this encoding and handle the surrogate pairs correctly.

Function: unicode:string-upcase string &key :start :end :casing ¶

Function: unicode:string-downcase string &key :start :end :casing ¶

The case of the string is changed appropriately. Surrogate pairs are handled correctly. The conversion to the appropriate case is done based on the Unicode conversion. The additional argument :casing controls how case conversion is done. The default value is :simple, which uses simple Unicode case conversion, which is equivalent to the same function in the COMMON-LISP package. If :casing is :full, then full Unicode case conversion is done where the string may actually increase in length.

Function: unicode:string-capitalize string &key :start ¶

:end :casing :unicode-word-break Given a string, returns a copy of the string with the first character of each “word” converted to upper-case, and remaining characters in the word converted to lower case. The value of :casing is :simple, :full or :title for simple, full or title case conversion, respectively. The default value for :casing is :title. If :unicode-word-break is non-Nil, then the Unicode word-breaking algorithm is used to determine the word boundaries. Otherwise, a “word” is defined to be a string of case-modifiable characters delimited by non-case-modifiable chars. The default for :unicode-word-break is T.

Function: nstring-upcase string &key :start :end ¶

Function: nstring-downcase string &key :start :end ¶

Function: nstring-capitalize string &key :start :end ¶

The case of the string is changed appropriately. Surrogate pairs are handled correctly. The conversion to the appropriate case is done based on the Unicode conversion. (Full casing is not available because the string length cannot be increased when needed.)

Function: string= s1 s2 &key :start1 :end1 :start2 :end2 ¶

Function: string/= s1 s2 &key :start1 :end1 :start2 :end2 ¶

Function: string< s1 s2 &key :start1 :end1 :start2 :end2 ¶

Function: string> s1 s2 &key :start1 :end1 :start2 :end2 ¶

Function: string<= s1 s2 &key :start1 :end1 :start2 :end2 ¶

Function: string>= s1 s2 &key :start1 :end1 :start2 :end2 ¶

The string comparison is done in codepoint order. (This is different from just comparing the order of the individual characters due to surrogate pairs.) Unicode collation is not done.

Function: string-equal s1 s2 &key :start1 :end1 :start2 :end2 ¶

Function: string-not-equal s1 s2 &key :start1 :end1 :start2 :end2 ¶

Function: string-lessp s1 s2 &key :start1 :end1 :start2 :end2 ¶

Function: string-greaterp s1 s2 &key :start1 :end1 :start2 :end2 ¶

Function: string-not-greaterp s1 s2 &key :start1 :end1 :start2 :end2 ¶

Function: string-not-lessp s1 s2 &key :start1 :end1 :start2 :end2 ¶

Each codepoint in each string is converted to lowercase and the appropriate comparison of the codepoint values is done. Unicode collation is not done.

Function: string-left-trim bag string ¶

Function: string-right-trim bag string ¶

Function: string-trim bag string ¶

Removes any characters in bag from the left, right, or both ends of the string string, respectively. This has potential problems if you want to remove a surrogate character from the string, since a single character cannot represent a surrogate. As an extension, if bag is a string, we properly handle surrogate characters in the bag.