1erl_eterm(3) C Library Functions erl_eterm(3)
2
6 erl_eterm - Functions for Erlang term construction.
7
9 Note:
10 The support for VxWorks is deprecated as of OTP 22, and will be removed
11 in OTP 23.
12 Note:
15 The old legacy erl_interface library (functions with prefix erl_) is
16 deprecated as of OTP 22, and will be removed in OTP 23. This does not
17 apply to the ei library. Reasonably new gcc compilers will issue depre‐
18 cation warnings. In order to disable these warnings, define the macro
19 EI_NO_DEPR_WARN.
20 This module provides functions for creating and manipulating Erlang
23 terms.
24 An Erlang term is represented by a C structure of type ETERM. Applica‐
26 tions should not reference any fields in this structure directly, as it
27 can be changed in future releases to provide faster and more compact
28 term storage. Instead, applications should use the macros and functions
29 provided.
30 Each of the following macros takes a single ETERM pointer as an argu‐
32 ment. The macros return a non-zero value if the test is true, otherwise
33 0.
34 ERL_IS_INTEGER(t):
36 True if t is an integer.
37 ERL_IS_UNSIGNED_INTEGER(t):
39 True if t is an integer.
40 ERL_IS_FLOAT(t):
42 True if t is a floating point number.
43 ERL_IS_ATOM(t):
45 True if t is an atom.
46 ERL_IS_PID(t):
48 True if t is a pid (process identifier).
49 ERL_IS_PORT(t):
51 True if t is a port.
52 ERL_IS_REF(t):
54 True if t is a reference.
55 ERL_IS_TUPLE(t):
57 True if t is a tuple.
58 ERL_IS_BINARY(t):
60 True if t is a binary.
61 ERL_IS_LIST(t):
63 True if t is a list with zero or more elements.
64 ERL_IS_EMPTY_LIST(t):
66 True if t is an empty list.
67 ERL_IS_CONS(t):
69 True if t is a list with at least one element.
70 The following macros can be used for retrieving parts of Erlang terms.
72 None of these do any type checking. Results are undefined if you pass
73 an ETERM* containing the wrong type. For example, passing a tuple to
74 ERL_ATOM_PTR() likely results in garbage.
75 char *ERL_ATOM_PTR(t):
77 char *ERL_ATOM_PTR_UTF8(t):
80 A string representing atom t.
81 int ERL_ATOM_SIZE(t):
83 int ERL_ATOM_SIZE_UTF8(t):
86 The length (in bytes) of atom t.
87 void *ERL_BIN_PTR(t):
89 A pointer to the contents of t.
90 int ERL_BIN_SIZE(t):
92 The length (in bytes) of binary object t.
93 int ERL_INT_VALUE(t):
95 The integer of t.
96 unsigned int ERL_INT_UVALUE(t):
98 The unsigned integer value of t.
99 double ERL_FLOAT_VALUE(t):
101 The floating point value of t.
102 ETERM *ERL_PID_NODE(t):
104 ETERM *ERL_PID_NODE_UTF8(t):
107 The node in pid t.
108 int ERL_PID_NUMBER(t):
110 The sequence number in pid t.
111 int ERL_PID_SERIAL(t):
113 The serial number in pid t.
114 int ERL_PID_CREATION(t):
116 The creation number in pid t.
117 int ERL_PORT_NUMBER(t):
119 The sequence number in port t.
120 int ERL_PORT_CREATION(t):
122 The creation number in port t.
123 ETERM *ERL_PORT_NODE(t):
125 ETERM *ERL_PORT_NODE_UTF8(t):
128 The node in port t.
129 int ERL_REF_NUMBER(t):
131 The first part of the reference number in ref t. Use only for com‐
132 patibility.
133 int ERL_REF_NUMBERS(t):
135 Pointer to the array of reference numbers in ref t.
136 int ERL_REF_LEN(t):
138 The number of used reference numbers in ref t.
139 int ERL_REF_CREATION(t):
141 The creation number in ref t.
142 int ERL_TUPLE_SIZE(t):
144 The number of elements in tuple t.
145 ETERM *ERL_CONS_HEAD(t):
147 The head element of list t.
148 ETERM *ERL_CONS_TAIL(t):
150 A list representing the tail elements of list t.
151
153 ETERM *erl_cons(head, tail)
154 Types:
156 ETERM *head;
158 ETERM *tail;
159 Concatenates two Erlang terms, prepending head onto tail and
161 thereby creating a cons cell. To make a proper list, tail is
162 always to be a list or an empty list. Notice that NULL is not a
163 valid list.
164 * head is the new term to be added.
166 * tail is the existing list to which head is concatenated.
168 The function returns a new list.
170 ERL_CONS_HEAD(list) and ERL_CONS_TAIL(list) can be used to
172 retrieve the head and tail components from the list.
173 erl_hd(list) and erl_tl(list) do the same thing, but check that
174 the argument really is a list.
175 Example:
177 ETERM *list,*anAtom,*anInt;
179 anAtom = erl_mk_atom("madonna");
180 anInt = erl_mk_int(21);
181 list = erl_mk_empty_list();
182 list = erl_cons(anAtom, list);
183 list = erl_cons(anInt, list);
184 ... /* do some work */
185 erl_free_compound(list);
186 ETERM *erl_copy_term(term)
189 Types:
191 ETERM *term;
193 Creates and returns a copy of the Erlang term term.
195 ETERM *erl_element(position, tuple)
197 Types:
199 int position;
201 ETERM *tuple;
202 Extracts a specified element from an Erlang tuple.
204 * position specifies which element to retrieve from tuple. The
206 elements are numbered starting from 1.
207 * tuple is an Erlang term containing at least position ele‐
209 ments.
210 Returns a new Erlang term corresponding to the requested ele‐
212 ment, or NULL if position was greater than the arity of tuple.
213 ETERM *erl_hd(list)
215 Types:
217 ETERM *list;
219 Extracts the first element from a list.
221 list is an Erlang term containing a list.
223 Returns an Erlang term corresponding to the head head element in
225 the list, or a NULL pointer if list was not a list.
226 void erl_init(NULL, 0)
228 Types:
230 void *NULL;
232 int 0;
233 This function must be called before any of the others in the
235 Erl_Interface library to initialize the library functions. The
236 arguments must be specified as erl_init(NULL,0).
237 int erl_iolist_length(list)
239 Types:
241 ETERM *list;
243 Returns the length of an I/O list.
245 list is an Erlang term containing an I/O list.
247 Returns the length of list, or -1 if list is not an I/O list.
249 For the definition of an I/O list, see erl_iolist_to_binary.
251 ETERM *erl_iolist_to_binary(term)
253 Types:
255 ETERM *list;
257 Converts an I/O list to a binary term.
259 list is an Erlang term containing a list.
261 Returns an Erlang binary term, or NULL if list was not an I/O
263 list.
264 Informally, an I/O list is a deep list of characters and bina‐
266 ries that can be sent to an Erlang port. In BNF, an I/O list is
267 formally defined as follows:
268 iolist ::= []
270 | Binary
271 | [iohead | iolist]
272 ;
273 iohead ::= Binary
274 | Byte (integer in the range [0..255])
275 | iolist
276 ;
277 char *erl_iolist_to_string(list)
280 Types:
282 ETERM *list;
284 Converts an I/O list to a NULL-terminated C string.
286 list is an Erlang term containing an I/O list. The I/O list must
288 not contain the integer 0, as C strings may not contain this
289 value except as a terminating marker.
290 Returns a pointer to a dynamically allocated buffer containing a
292 string. If list is not an I/O list, or if list contains the
293 integer 0, NULL is returned. It is the caller's responsibility
294 to free the allocated buffer with erl_free().
295 For the definition of an I/O list, see erl_iolist_to_binary.
297 int erl_length(list)
299 Types:
301 ETERM *list;
303 Determines the length of a proper list.
305 list is an Erlang term containing a proper list. In a proper
307 list, all tails except the last point to another list cell, and
308 the last tail points to an empty list.
309 Returns -1 if list is not a proper list.
311 ETERM *erl_mk_atom(string)
313 Types:
315 const char *string;
317 Creates an atom.
319 string is the sequence of characters that will be used to create
321 the atom.
322 Returns an Erlang term containing an atom. Notice that it is the
324 caller's responsibility to ensure that string contains a valid
325 name for an atom.
326 ERL_ATOM_PTR(atom) and ERL_ATOM_PTR_UTF8(atom) can be used to
328 retrieve the atom name (as a NULL-terminated string).
329 ERL_ATOM_SIZE(atom) and ERL_ATOM_SIZE_UTF8(atom) return the
330 length of the atom name.
331 Note:
333 The UTF-8 variants were introduced in Erlang/OTP R16 and the
334 string returned by ERL_ATOM_PTR(atom) was not NULL-terminated on
335 older releases.
336 ETERM *erl_mk_binary(bptr, size)
339 Types:
341 char *bptr;
343 int size;
344 Produces an Erlang binary object from a buffer containing a
346 sequence of bytes.
347 * bptr is a pointer to a buffer containing data to be con‐
349 verted.
350 * size indicates the length of bptr.
352 Returns an Erlang binary object.
354 ERL_BIN_PTR(bin) retrieves a pointer to the binary data.
356 ERL_BIN_SIZE(bin) retrieves the size.
357 ETERM *erl_mk_empty_list()
359 Creates and returns an empty Erlang list. Notice that NULL is
361 not used to represent an empty list; Use this function instead.
362 ETERM *erl_mk_estring(string, len)
364 Types:
366 char *string;
368 int len;
369 Creates a list from a sequence of bytes.
371 * string is a buffer containing a sequence of bytes. The buf‐
373 fer does not need to be NULL-terminated.
374 * len is the length of string.
376 Returns an Erlang list object corresponding to the character
378 sequence in string.
379 ETERM *erl_mk_float(f)
381 Types:
383 double f;
385 Creates an Erlang float.
387 f is a value to be converted to an Erlang float.
389 Returns an Erlang float object with the value specified in f or
391 NULL if f is not finite.
392 ERL_FLOAT_VALUE(t) can be used to retrieve the value from an
394 Erlang float.
395 ETERM *erl_mk_int(n)
397 Types:
399 int n;
401 Creates an Erlang integer.
403 n is a value to be converted to an Erlang integer.
405 Returns an Erlang integer object with the value specified in n.
407 ERL_INT_VALUE(t) can be used to retrieve the value from an
409 Erlang integer.
410 ETERM *erl_mk_list(array, arrsize)
412 Types:
414 ETERM **array;
416 int arrsize;
417 Creates an Erlang list from an array of Erlang terms, such that
419 each element in the list corresponds to one element in the
420 array.
421 * array is an array of Erlang terms.
423 * arrsize is the number of elements in array.
425 The function creates an Erlang list object, whose length arrsize
427 and whose elements are taken from the terms in array.
428 ETERM *erl_mk_long_ref(node, n1, n2, n3, creation)
430 Types:
432 const char *node;
434 unsigned int n1, n2, n3;
435 unsigned int creation;
436 Creates an Erlang reference, with 82 bits.
438 * node is the name of the C-node.
440 * n1, n2, and n3 can be seen as one big number
442 n1*2^64+n2*2^32+n3, which is to be chosen uniquely for each
443 reference created for a given C-node.
444 * creation is an arbitrary number.
446 Notice that n3 and creation are limited in precision, so only
448 the low 18 and 2 bits of these numbers are used.
449 Returns an Erlang reference object.
451 ERL_REF_NODE(ref), ERL_REF_NUMBERS(ref), ERL_REF_LEN(ref), and
453 ERL_REF_CREATION(ref) can be used to retrieve the values used to
454 create the reference.
455 ETERM *erl_mk_pid(node, number, serial, creation)
457 Types:
459 const char *node;
461 unsigned int number;
462 unsigned int serial;
463 unsigned int creation;
464 Creates an Erlang process identifier (pid). The resulting pid
466 can be used by Erlang processes wishing to communicate with the
467 C-node.
468 * node is the name of the C-node.
470 * number, serial, and creation are arbitrary numbers. Notice
472 that these are limited in precision, so only the low 15, 3,
473 and 2 bits of these numbers are used.
474 Returns an Erlang pid object.
476 ERL_PID_NODE(pid), ERL_PID_NUMBER(pid), ERL_PID_SERIAL(pid), and
478 ERL_PID_CREATION(pid) can be used to retrieve the four values
479 used to create the pid.
480 ETERM *erl_mk_port(node, number, creation)
482 Types:
484 const char *node;
486 unsigned int number;
487 unsigned int creation;
488 Creates an Erlang port identifier.
490 * node is the name of the C-node.
492 * number and creation are arbitrary numbers. Notice that these
494 are limited in precision, so only the low 18 and 2 bits of
495 these numbers are used.
496 Returns an Erlang port object.
498 ERL_PORT_NODE(port), ERL_PORT_NUMBER(port), and ERL_PORT_CRE‐
500 ATION can be used to retrieve the three values used to create
501 the port.
502 ETERM *erl_mk_ref(node, number, creation)
504 Types:
506 const char *node;
508 unsigned int number;
509 unsigned int creation;
510 Creates an old Erlang reference, with only 18 bits - use
512 erl_mk_long_ref instead.
513 * node is the name of the C-node.
515 * number is to be chosen uniquely for each reference created
517 for a given C-node.
518 * creation is an arbitrary number.
520 Notice that number and creation are limited in precision, so
522 only the low 18 and 2 bits of these numbers are used.
523 Returns an Erlang reference object.
525 ERL_REF_NODE(ref), ERL_REF_NUMBER(ref), and ERL_REF_CRE‐
527 ATION(ref) can be used to retrieve the three values used to cre‐
528 ate the reference.
529 ETERM *erl_mk_string(string)
531 Types:
533 char *string;
535 Creates a list from a NULL-terminated string.
537 string is a NULL-terminated sequence of characters (that is, a C
539 string) from which the list will be created.
540 Returns an Erlang list.
542 ETERM *erl_mk_tuple(array, arrsize)
544 Types:
546 ETERM **array;
548 int arrsize;
549 Creates an Erlang tuple from an array of Erlang terms.
551 * array is an array of Erlang terms.
553 * arrsize is the number of elements in array.
555 The function creates an Erlang tuple, whose arity is size and
557 whose elements are taken from the terms in array.
558 To retrieve the size of a tuple, either use function erl_size
560 (which checks the type of the checked term and works for a
561 binary as well as for a tuple) or ERL_TUPLE_SIZE(tuple) returns
562 the arity of a tuple. erl_size() does the same thing, but it
563 checks that the argument is a tuple. erl_element(index,tuple)
564 returns the element corresponding to a given position in the
565 tuple.
566 ETERM *erl_mk_uint(n)
568 Types:
570 unsigned int n;
572 Creates an Erlang unsigned integer.
574 n is a value to be converted to an Erlang unsigned integer.
576 Returns an Erlang unsigned integer object with the value speci‐
578 fied in n.
579 ERL_INT_UVALUE(t) can be used to retrieve the value from an
581 Erlang unsigned integer.
582 ETERM *erl_mk_var(name)
584 Types:
586 char *name;
588 Creates an unbound Erlang variable. The variable can later be
590 bound through pattern matching or assignment.
591 name specifies a name for the variable.
593 Returns an Erlang variable object with the name name.
595 int erl_print_term(stream, term)
597 Types:
599 FILE *stream;
601 ETERM *term;
602 Prints the specified Erlang term to the specified output stream.
604 * stream indicates where the function is to send its output.
606 * term is the Erlang term to print.
608 Returns the number of characters written on success, otherwise a
610 negative value.
611 void erl_set_compat_rel(release_number)
613 Types:
615 unsigned release_number;
617 By default, the Erl_Interface library is only guaranteed to be
619 compatible with other Erlang/OTP components from the same
620 release as the Erl_Interface library itself. For example,
621 Erl_Interface from Erlang/OTP R10 is not compatible with an
622 Erlang emulator from Erlang/OTP R9 by default.
623 A call to erl_set_compat_rel(release_number) sets the Erl_Inter‐
625 face library in compatibility mode of release release_number.
626 Valid range of release_number is [7, current release]. This
627 makes it possible to communicate with Erlang/OTP components from
628 earlier releases.
629 Note:
631 If this function is called, it may only be called once directly
632 after the call to function erl_init().
633 Warning:
636 You may run into trouble if this feature is used carelessly.
637 Always ensure that all communicating components are either from
638 the same Erlang/OTP release, or from release X and release Y
639 where all components from release Y are in compatibility mode of
640 release X.
641 int erl_size(term)
644 Types:
646 ETERM *term;
648 Returns either the arity of an Erlang tuple or the number of
650 bytes in an Erlang binary object.
651 term is an Erlang tuple or an Erlang binary object.
653 Returns the size of term as described above, or -1 if term is
655 not one of the two supported types.
656 ETERM *erl_tl(list)
658 Types:
660 ETERM *list;
662 Extracts the tail from a list.
664 list is an Erlang term containing a list.
666 Returns an Erlang list corresponding to the original list minus
668 the first element, or NULL pointer if list was not a list.
669 ETERM *erl_var_content(term, name)
671 Types:
673 ETERM *term;
675 char *name;
676 Returns the contents of the specified variable in an Erlang
678 term.
679 * term is an Erlang term. In order for this function to suc‐
681 ceed, term must either be an Erlang variable with the speci‐
682 fied name, or it must be an Erlang list or tuple containing
683 a variable with the specified name. Other Erlang types can‐
684 not contain variables.
685 * name is the name of an Erlang variable.
687 Returns the Erlang object corresponding to the value of name in
689 term. If no variable with the name name is found in term, or if
690 term is not a valid Erlang term, NULL is returned.
691Ericsson AB erl_interface 3.13 erl_eterm(3)