The functions PL_get_*() read information from a Prolog
term. Most of them take two arguments. The first is the input term and
the second is a pointer to the output value or a term reference.
- int PL_get_atom(term_t
+t, atom_t *a)
- If t is an atom, store the unique atom identifier over a.
See also PL_atom_chars()
and PL_new_atom().
If there is no need to access the data (characters) of an atom, it is
advised to manipulate atoms using their handle. As the atom is
referenced by t, it will live at least as long as t
does. If longer live-time is required, the atom should be locked using PL_register_atom().
- int PL_get_atom_chars(term_t
+t, char **s)
- If t is an atom, store a pointer to a 0-terminated C-string
in
s. It is explicitly not allowed to modify
the contents of this string. Some built-in atoms may have the string
allocated in read-only memory, so `temporary manipulation' can cause an
error.
- int PL_get_string_chars(term_t
+t, char **s, size_t *len)
- If t is a string object, store a pointer to a 0-terminated
C-string in s and the length of the string in len.
Note that this pointer is invalidated by backtracking, garbage
collection and stack-shifts, so generally the only save operations are
to pass it immediately to a C function that doesn't involve Prolog.
- int PL_get_chars(term_t
+t, char **s, unsigned flags)
- Convert the argument term t to a 0-terminated C-string. flags
is a bitwise disjunction from two groups of constants. The first
specifies which term types should be converted and the second how the
argument is stored. Below is a specification of these constants.
BUF_RING
implies, if the data is not static (as from an atom), that the data is
copied to the next buffer from a ring of 16 buffers. This is a
convenient way of converting multiple arguments passed to a foreign
predicate to C-strings. If BUF_MALLOC is used, the data must be freed
using PL_free()
when no longer needed.
With the introduction of wide characters (see section
2.19.1), not all atoms can be converted into a char*.
This function fails if t is of the wrong type, but also if
the text cannot be represented. See the REP_* flags below
for details.
- CVT_ATOM
- Convert if term is an atom.
- CVT_STRING
- Convert if term is a string.
- CVT_LIST
- Convert if term is a list of of character codes.
- CVT_INTEGER
- Convert if term is an integer.
- CVT_FLOAT
- Convert if term is a float. The characters returned are the same as
write/1
would write for the floating point number.
- CVT_NUMBER
- Convert if term is an integer or float.
- CVT_ATOMIC
- Convert if term is atomic.
- CVT_VARIABLE
- Convert variable to print-name
- CVT_WRITE
- Convert any term that is not converted by any of the other flags using
write/1.
If no
BUF_* is provided, BUF_RING is implied.
- CVT_WRITE_CANONICAL
- As
CVT_WRITE, but using write_canonical/2.
- CVT_WRITEQ
- As
CVT_WRITE, but using writeq/2.
- CVT_ALL
- Convert if term is any of the above, except for
CVT_VARIABLE
and
CVT_WRITE*.
- CVT_EXCEPTION
- If conversion fails due to a type error, raise a Prolog type error
exception in addition to failure
- BUF_DISCARDABLE
- Data must copied immediately
- BUF_RING
- Data is stored in a ring of buffers
- BUF_MALLOC
- Data is copied to a new buffer returned by PL_malloc(3).
When no longer needed the user must call PL_free()
on the data.
- REP_ISO_LATIN_1
- Text is in ISO Latin-1 encoding and the call fails if text cannot be
represented. This flag has the value 0 and is thus the default.
- REP_UTF8
- Convert the text to a UTF-8 string. This works for all text.
- REP_MB
- Convert to default locale-defined 8-bit string. Success depends on the
locale. Conversion is done using the wcrtomb() C library function.
- int PL_get_list_chars(+term_t
l, char **s, unsigned flags)
- Same as
PL_get_chars(l, s,
CVT_LIST|flags), provided flags
contains none of the CVT_* flags.
- int PL_get_integer(+term_t
t, int *i)
- If t is a Prolog integer, assign its value over i.
On 32-bit machines, this is the same as PL_get_long(),
but avoids a warning from the compiler. See also PL_get_long().
- int PL_get_long(term_t
+t, long *i)
- If t is a Prolog integer that can be represented as a long,
assign its value over i. If t is an integer that
cannot be represented by a C long, this function returns
FALSE.
If t is a floating point number that can be represented as a
long, this function succeeds as well. See also PL_get_int64().
- int PL_get_int64(term_t
+t, int64_t *i)
- If t is a Prolog integer or float that can be represented as
a
int64_t, assign its value over i.
- int PL_get_intptr(term_t
+t, intptr_t *i)
- Get an integer that is at least as wide as a pointer. On most platforms
this is the same as PL_get_long(),
but on Win64 pointers are 8 bytes and longs only 4. Unlike PL_get_pointer(),
the value is not modified.
- int PL_get_bool(term_t
+t, int *val)
- If t has the value
true or false,
set val to the C constant TRUE or FALSE
and return success, otherwise return failure.
- int PL_get_pointer(term_t
+t, void **ptr)
- In the current system, pointers are represented by Prolog integers, but
need some manipulation to make sure they do not get truncated due to the
limited Prolog integer range. PL_put_pointer()
and PL_get_pointer()
guarantee pointers in the range of malloc() are handled without
truncating.
- int PL_get_float(term_t
+t, double *f)
- If t is a float or integer, its value is assigned over f.
- int PL_get_functor(term_t
+t, functor_t *f)
- If t is compound or an atom, the Prolog representation of the
name-arity pair will be assigned over f. See also
PL_get_name_arity()
and PL_is_functor().
- int PL_get_name_arity(term_t
+t, atom_t *name, size_t *arity)
- If t is compound or an atom, the functor name will be
assigned over name and the arity over arity. See
also
PL_get_functor()
and PL_is_functor().
See section
12.3.2.1.
- int PL_get_compound_name_arity(term_t
+t, atom_t *name, size_t *arity)
- If t is compound term, the functor name will be assigned over
name and the arity over arity. This is the same as
PL_get_name_arity(),
but this function fails if t is an atom.
- int PL_get_module(term_t
+t, module_t *module)
- If t is an atom, the system will look up or create the
corresponding module and assign an opaque pointer to it over module.
- int PL_get_arg(size_t
index, term_t +t, term_t -a)
- If t is compound and index is between 1 and arity
(inclusive), assign a with a term reference to the argument.
- int _PL_get_arg(size_t
index, term_t +t, term_t -a)
- Same as PL_get_arg(),
but no checking is performed, neither whether t is actually a
term nor whether index is a valid argument index.