loat, integer or rational number, its value is assigned over f. Note that if t is an integer or rational conversion may fail because the number cannot be represented as a float.

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 (either or both may be NULL). See also PL_get_functor() and PL_is_functor().

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.

int PL_get_dict_key(atom_t key, term_t +dict, term_t -value)

If dict is a dict, get the associated value in value. Fails silently if key does not appear in dict or if if dict is not a dict.

12.4.4.3 Exchanging text using length and string

All internal text representation in SWI-Prolog is represented using char * plus length and allow for 0-bytes in them. The foreign library supports this by implementing a *_nchars() function for each applicable *_chars() function. Below we briefly present the signatures of these functions. For full documentation consult the *_chars() function.

int PL_get_atom_nchars(term_t t, size_t *len, char **s)

See PL_get_atom_chars().

int PL_get_list_nchars(term_t t, size_t *len, char **s)

See PL_get_list_chars().

int PL_get_nchars(term_t t, size_t *len, char **s, unsigned int flags)

See PL_get_chars(). The len pointer may be NULL.

int PL_put_atom_nchars(term_t t, s