Support for exchange of wide-character strings is still under
consideration. The functions dealing with 8-bit character strings return
failure when operating on a wide-character atom or Prolog string object.
The functions below can extract and unify both 8-bit and wide atoms and
string objects. Wide character strings are represented as C arrays of
objects of the type pl_wchar_t, which is guaranteed to be
the same as wchar_t on platforms supporting this type. For
example, on MS-Windows, this represents a 16-bit UTF-16 string, while
using the GNU C library (glibc) this represents 32-bit UCS4 characters.
- atom_t PL_new_atom_wchars(size_t
len, const pl_wchar_t *s)
- Create atom from wide-character string as PL_new_atom_nchars()
does for ISO-Latin-1 strings. If s only contains ISO-Latin-1
characters a normal byte-array atom is created. If len is
(size_t)-1,
it is computed from s using wcslen(). See PL_new_atom()
for error handling.
- const pl_wchar_t* PL_atom_wchars(atom_t
atom, size_t *len)
- Extract characters from a wide-character atom. Succeeds on any atom
marked as‘text’. If the underlying atom is a wide-character
atom, the returned pointer is a pointer into the atom structure. If the
atom is represented as an ISO-Latin-1 string, the returned pointer comes
from Prolog's‘buffer stack’(see section
12.4.14).
- bool PL_get_wchars(term_t
t, size_t *len, pl_wchar_t **s, unsigned flags)
- Wide-character version of PL_get_chars().
The flags argument is the same as for PL_get_chars().
Note that this operation may return a pointer into Prolog's‘buffer
stack’(see section
12.4.14).
- bool PL_put_wchars(term_t
-t, int type, size_t len, const pl_wchar_t *s)
- Put text from a wide character array in t. Arguments
are the same as PL_unify_wchars().219The
current implementation uses PL_put_variable()
followed by PL_unify_wchars().
- bool PL_unify_wchars(term_t
+t, int type, size_t len, const pl_wchar_t *s)
- Unify t with a textual representation of the C wide-character
array s. The type argument defines the Prolog
representation and is one of
PL_ATOM, PL_STRING,
PL_CODE_LIST or PL_CHAR_LIST.
- bool PL_unify_wchars_diff(term_t
+t, term_t -tail, int type, size_t len, const pl_wchar_t *s)
- Difference list version of PL_unify_wchars(),
only supporting the types
PL_CODE_LIST and PL_CHAR_LIST.
It serves two purposes. It allows for returning very long lists from
data read from a stream without the need for a resizing buffer in C.
Also, the use of difference lists is often practical for further
processing in Prolog. Examples can be found in packages/clib/readutil.c
from the source distribution.
- int PL_wcwidth(int
chr)
- Display column width of a Unicode code point chr. Returns 0
for combining and other zero-width characters, 2 for East Asian Wide and
Fullwidth characters, 1 for ordinary printable characters, and -1 for
control characters and code points unknown to the implementation.
The result is locale-independent and identical on every supported
platform. Width data is sourced at table-build time from
EastAsianWidth.txt (UAX #11) and the general-category
property, and stored as two bits in each uflags_map entry
alongside the syntax classification used by the parser; runtime lookups
are a single byte fetch. The Unicode version that drives the table is
reported by the unicode_syntax_version
flag (see
section 2.15.1.9).
The argument is a full 32-bit code point. Avoid casting to
wchar_t before the call: wchar_t is 16-bit on
Windows, and the cast silently drops non-BMP characters.
- int PL_is_id_start(int
chr)
- int PL_is_id_continue(int
chr)
- int PL_is_uppercase(int
chr)
- int PL_is_decimal(int
chr)
- int PL_is_layout(int
chr)
- Unicode classification predicates. Each returns non-zero iff the 32-bit
code point chr carries the corresponding property as defined
by the data files in
src/Unicode/ and consulted by the
Prolog reader. Provided so foreign extensions and embedded toolkits
(notably xpce) classify code points exactly as SWI-Prolog does, locale-
independently. id_start and id_continue follow
Prolog's identifier syntax (close to UAX #31 XID_Start /
XID_Continue, adjusted for Prolog). layout matches the
reader's whitespace set (white_space/1 in
src/Unicode/derived_core_properties.pl).
