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| unsigned char | glk_char_to_lower () |
| unsigned char | glk_char_to_upper () |
| glui32 | glk_buffer_to_lower_case_uni () |
| glui32 | glk_buffer_to_upper_case_uni () |
| glui32 | glk_buffer_to_title_case_uni () |
Glk has functions to manipulate the case of both Latin-1 and Unicode strings. One Latin-1 lowercase character corresponds to one uppercase character, and vice versa, so the Latin-1 functions act on single characters. The Unicode functions act on whole strings, since the length of the string may change.
unsigned char
glk_char_to_lower (unsigned char ch);
You can convert Latin-1 characters between upper and lower case with two Glk
utility functions, glk_char_to_lower() and glk_char_to_upper(). These have a
few advantages over the standard ANSI tolower()toupper()glk_char_to_lower() on a lower-case character, or a
character which is not a letter, you'll get the argument back unchanged.
The case-sensitive characters in Latin-1 are the ranges 0x41..0x5A,
0xC0..0xD6, 0xD8..0xDE (upper case) and the ranges 0x61..0x7A, 0xE0..0xF6,
0xF8..0xFE (lower case). These are arranged in parallel; so
glk_char_to_lower() will add 0x20 to values in the upper-case ranges, and
glk_char_to_upper() will subtract 0x20 from values in the lower-case ranges.
unsigned char
glk_char_to_upper (unsigned char ch);
If ch
is a lowercase character in the Latin-1 character set, converts it to
uppercase. Otherwise, leaves it unchanged. See glk_char_to_lower().
glui32 glk_buffer_to_lower_case_uni (glui32 *buf,glui32 len,glui32 numchars);
Unicode character conversion is trickier, and must be applied to character
arrays, not single characters. These functions
(glk_buffer_to_lower_case_uni(), glk_buffer_to_upper_case_uni(), and
glk_buffer_to_title_case_uni()) provide two length arguments because a
string of Unicode characters may expand when its case changes. The len
argument is the available length of the buffer; numchars
is the number of
characters in the buffer initially. (So numchars
must be less than or equal
to len
. The contents of the buffer after numchars
do not affect the
operation.)
The functions return the number of characters after conversion. If this is
greater than len
, the characters in the array will be safely truncated at
len
, but the true count will be returned. (The contents of the buffer after
the returned count are undefined.)
The lower_case and upper_case functions do what you'd expect: they
convert every character in the buffer (the first numchars
of them) to its
upper or lower-case equivalent, if there is such a thing.
See the Unicode spec (chapter 3.13, chapter 4.2, etc) for the exact definitions of upper, lower, and title-case mapping.
Unicode has some strange case cases. For example, a combined character
that looks like “ss” might properly be upper-cased into
two “S” characters.
Title-casing is even stranger; “ss” (at the beginning of a word) might be
title-cased into a different combined character that looks like “Ss”.
The glk_buffer_to_title_case_uni() function is actually title-casing the
first character of the buffer.
If it makes a difference.
glui32 glk_buffer_to_upper_case_uni (glui32 *buf,glui32 len,glui32 numchars);
Converts the first numchars
characters of buf
to their uppercase
equivalents, if there is such a thing. See glk_buffer_to_lower_case_uni().
glui32 glk_buffer_to_title_case_uni (glui32 *buf,glui32 len,glui32 numchars,glui32 lowerrest);
See glk_buffer_to_lower_case_uni(). The title_case function has an
additional (boolean) flag. If the flag is zero, the function changes the
first character of the buffer to upper-case, and leaves the rest of the
buffer unchanged. If the flag is nonzero, it changes the first character to
upper-case and the rest to lower-case.
Earlier drafts of this spec had a separate function which title-cased the first character of every word in the buffer. I took this out after reading Unicode Standard Annex #29, which explains how to divide a string into words. If you want it, feel free to implement it.