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8.2.52 string ¶

Class: string ¶

A string array of Unicode strings.

A string array is an array of strings, where each array element is a single string.

The string class represents strings, where:

• Each element of a string array is a single string
• A single string is a 1-dimensional row vector of Unicode characters
• Those characters are encoded in UTF-8
  • This last bit depends on the fact that Octave chars are UTF-8 now

This should correspond pretty well to what people think of as strings, and is pretty compatible with people’s typical notion of strings in Octave.

String arrays also have a special “missing” value, that is like the string equivalent of NaN for doubles or “undefined” for categoricals, or SQL NULL.

This is a slightly higher-level and more strongly-typed way of representing strings than cellstrs are. (A cellstr array is of type cell, not a text- specific type, and allows assignment of non-string data into it.)

Be aware that while string arrays interconvert with Octave chars and cellstrs, Octave char elements represent 8-bit UTF-8 code units, not Unicode code points.

This class really serves three roles:

1. It is a type-safe object wrapper around Octave’s base primitive character types.
2. It adds ismissing() semantics.
3. And it introduces Unicode support.

Not clear whether it’s a good fit to have the Unicode support wrapped up in this. Maybe it should just be a simple object wrapper wrapper, and defer Unicode semantics to when core Octave adopts them for char and cellstr. On the other hand, because Octave chars are UTF-8, not UCS-2, some methods like strlength() and reverse() are just going to be wrong if they delegate straight to chars.

“Missing” string values work like NaNs. They are never considered equal, less than, or greater to any other string, including other missing strings. This applies to set membership and other equivalence tests.

TODO: Need to decide how far to go with Unicode semantics, and how much to just make this an object wrapper over cellstr and defer to Octave’s existing char/string-handling functions.

TODO: demote_strings should probably be static or global, so that other functions can use it to hack themselves into being string-aware.

• string.empty
• string.missing
• string.string
• string.isstring
• string.dispstrs
• string.ismissing
• string.isnanny
• string.cellstr
• string.cell
• string.char
• string.encode
• string.strlength_bytes
• string.strlength
• string.reverse_bytes
• string.reverse
• string.strcat
• string.plus
• string.lower
• string.upper
• string.erase
• string.strrep
• string.strfind
• string.regexprep
• string.strcmp
• string.cmp
• string.decode