Example:
PREDICATE(test, 1)
{ PlAtom a1(A1);
if ( a1 == "read" )
...;
}
This approach extracts the atom once and for each test extracts the
represented string from the atom and compares it. It avoids the need for
global atom constructors.
- PlAtom :: PlAtom(atom_t handle)
- Create from C-interface atom handle (
atom_t). Used
internally and for integration with the C-interface.
- PlAtom :: PlAtom(const char *text, PlEncoding
rep=ENC_INPUT)
- PlAtom :: PlAtom(size_t len, const char *s,
PlEncoding rep=ENC_INPUT)
- PlAtom :: PlAtom(const wchar_t *text)
- PlAtom :: PlAtom(const std::string& text,
PlEncoding rep=ENC_INPUT)
- PlAtom :: PlAtom(const std::wstring& text)
- Create an atom from a string. The text is copied if a new
atom is created. For the
char* and std::string
forms
rep gives the byte encoding (see section
1.8.2); it defaults to ENC_INPUT. See PL_new_atom_mbchars()
and
PL_new_atom_wchars(). The constructors
PlAtom(PlEncoding, len, s)
and PlAtom(PlEncoding,
std::string&) are [[deprecated]] in favour
of the trailing-PlEncoding forms above.
- PlAtom :: PlAtom(const PlTerm &t)
- If t represents an atom, the new instance represents this
atom. Otherwise a
type_error is thrown.
- int PlAtom::operator
==(const wchar_t *text)
- int PlAtom::operator
==(const char *text)
- int PlAtom::operator
==(const std::string& text)
- int PlAtom::operator
==(const std::wstring& text)
- Yields
true if the atom represents text, false
otherwise. Performs a strcmp() or similar for this.
- int PlAtom::operator
==(const PlAtom &a)
- Compares the two atom-handles, returning
true or
false. Because atoms are unique, there is no need to use strcmp()
for this.
- int PlAtom::operator
!=(const wchar_t *text)
- int PlAtom::operator
!=(const char *text)
- int PlAtom::operator
!=(const std::string& text)
- int PlAtom::operator
!=(const std::wstring& text)
- int PlAtom::operator
!=(const PlAtom &a)
- The inverse of the
==
- bool is_valid()
- Verifies that the handle is valid. This can be used after calling a
function that returns an atom handle, to check that a new atom was
created.
- void reset()
- Sets the handle to an invalid valid - a subsequent call to is_null()
will return
true.
- const std::string as_string(PlEncoding
enc=ENC_OUTPUT)
- Returns the string representation of the atom.28If
you wish to return a
char* from a function, you should not
do return t.as_string().c_str()
because that will return a pointer into the stack (Gnu C++ or Clang
options -Wreturn-stack-address or -Wreturn-local-addr)
can sometimes catch this, as can the runtime address sanitizer
when run with detect_stack_use_after_return=1.
This does not quote or escape any characters that would need to be
escaped if the atom were to be input to the Prolog parser. The possible
values for enc are (see section
1.8.2):
PlEncoding::Latin1 - throws an exception if the text
cannot be represented in ISO Latin-1.PlEncoding::UTF8 - UTF-8.PlEncoding::Locale - uses the locale to determine the
representation.
The constants ENC_INPUT (PlEncoding::Latin1)
and
ENC_OUTPUT (PlEncoding::Locale) name the
defaults used for constructing and returning text respectively.
- const std:wstring as_wstring()
- Returns the string representation of the atom. This does not quote or
escape any characters that would need to be escaped if the atom were to
be input to the Prolog parser.
- void register_atom()
- See PL_register_atom().
- void unregister_atom()
- See PL_unregister_atom().
- void* blob_data(size_t
*len, struct PL_blob_t **type)
- See PL_blob_data().