1erl_eterm(3) C Library Functions erl_eterm(3)
2
6 erl_eterm - Functions for Erlang term construction.
7
9 This module provides functions for creating and manipulating Erlang
10 terms.
11 An Erlang term is represented by a C structure of type ETERM. Applica‐
13 tions should not reference any fields in this structure directly, as it
14 can be changed in future releases to provide faster and more compact
15 term storage. Instead, applications should use the macros and functions
16 provided.
17 Each of the following macros takes a single ETERM pointer as an argu‐
19 ment. The macros return a non-zero value if the test is true, otherwise
20 0.
21 ERL_IS_INTEGER(t):
23 True if t is an integer.
24 ERL_IS_UNSIGNED_INTEGER(t):
26 True if t is an integer.
27 ERL_IS_FLOAT(t):
29 True if t is a floating point number.
30 ERL_IS_ATOM(t):
32 True if t is an atom.
33 ERL_IS_PID(t):
35 True if t is a pid (process identifier).
36 ERL_IS_PORT(t):
38 True if t is a port.
39 ERL_IS_REF(t):
41 True if t is a reference.
42 ERL_IS_TUPLE(t):
44 True if t is a tuple.
45 ERL_IS_BINARY(t):
47 True if t is a binary.
48 ERL_IS_LIST(t):
50 True if t is a list with zero or more elements.
51 ERL_IS_EMPTY_LIST(t):
53 True if t is an empty list.
54 ERL_IS_CONS(t):
56 True if t is a list with at least one element.
57 The following macros can be used for retrieving parts of Erlang terms.
59 None of these do any type checking. Results are undefined if you pass
60 an ETERM* containing the wrong type. For example, passing a tuple to
61 ERL_ATOM_PTR() likely results in garbage.
62 char *ERL_ATOM_PTR(t):
64 char *ERL_ATOM_PTR_UTF8(t):
67 A string representing atom t.
68 int ERL_ATOM_SIZE(t):
70 int ERL_ATOM_SIZE_UTF8(t):
73 The length (in bytes) of atom t.
74 void *ERL_BIN_PTR(t):
76 A pointer to the contents of t.
77 int ERL_BIN_SIZE(t):
79 The length (in bytes) of binary object t.
80 int ERL_INT_VALUE(t):
82 The integer of t.
83 unsigned int ERL_INT_UVALUE(t):
85 The unsigned integer value of t.
86 double ERL_FLOAT_VALUE(t):
88 The floating point value of t.
89 ETERM *ERL_PID_NODE(t):
91 ETERM *ERL_PID_NODE_UTF8(t):
94 The node in pid t.
95 int ERL_PID_NUMBER(t):
97 The sequence number in pid t.
98 int ERL_PID_SERIAL(t):
100 The serial number in pid t.
101 int ERL_PID_CREATION(t):
103 The creation number in pid t.
104 int ERL_PORT_NUMBER(t):
106 The sequence number in port t.
107 int ERL_PORT_CREATION(t):
109 The creation number in port t.
110 ETERM *ERL_PORT_NODE(t):
112 ETERM *ERL_PORT_NODE_UTF8(t):
115 The node in port t.
116 int ERL_REF_NUMBER(t):
118 The first part of the reference number in ref t. Use only for com‐
119 patibility.
120 int ERL_REF_NUMBERS(t):
122 Pointer to the array of reference numbers in ref t.
123 int ERL_REF_LEN(t):
125 The number of used reference numbers in ref t.
126 int ERL_REF_CREATION(t):
128 The creation number in ref t.
129 int ERL_TUPLE_SIZE(t):
131 The number of elements in tuple t.
132 ETERM *ERL_CONS_HEAD(t):
134 The head element of list t.
135 ETERM *ERL_CONS_TAIL(t):
137 A list representing the tail elements of list t.
138
140 ETERM *erl_cons(head, tail)
141 Types:
143 ETERM *head;
145 ETERM *tail;
146 Concatenates two Erlang terms, prepending head onto tail and
148 thereby creating a cons cell. To make a proper list, tail is
149 always to be a list or an empty list. Notice that NULL is not a
150 valid list.
151 * head is the new term to be added.
153 * tail is the existing list to which head is concatenated.
155 The function returns a new list.
157 ERL_CONS_HEAD(list) and ERL_CONS_TAIL(list) can be used to
159 retrieve the head and tail components from the list.
160 erl_hd(list) and erl_tl(list) do the same thing, but check that
161 the argument really is a list.
162 Example:
164 ETERM *list,*anAtom,*anInt;
166 anAtom = erl_mk_atom("madonna");
167 anInt = erl_mk_int(21);
168 list = erl_mk_empty_list();
169 list = erl_cons(anAtom, list);
170 list = erl_cons(anInt, list);
171 ... /* do some work */
172 erl_free_compound(list);
173 ETERM *erl_copy_term(term)
176 Types:
178 ETERM *term;
180 Creates and returns a copy of the Erlang term term.
182 ETERM *erl_element(position, tuple)
184 Types:
186 int position;
188 ETERM *tuple;
189 Extracts a specified element from an Erlang tuple.
191 * position specifies which element to retrieve from tuple. The
193 elements are numbered starting from 1.
194 * tuple is an Erlang term containing at least position ele‐
196 ments.
197 Returns a new Erlang term corresponding to the requested ele‐
199 ment, or NULL if position was greater than the arity of tuple.
200 ETERM *erl_hd(list)
202 Types:
204 ETERM *list;
206 Extracts the first element from a list.
208 list is an Erlang term containing a list.
210 Returns an Erlang term corresponding to the head head element in
212 the list, or a NULL pointer if list was not a list.
213 void erl_init(NULL, 0)
215 Types:
217 void *NULL;
219 int 0;
220 This function must be called before any of the others in the
222 Erl_Interface library to initialize the library functions. The
223 arguments must be specified as erl_init(NULL,0).
224 int erl_iolist_length(list)
226 Types:
228 ETERM *list;
230 Returns the length of an I/O list.
232 list is an Erlang term containing an I/O list.
234 Returns the length of list, or -1 if list is not an I/O list.
236 For the definition of an I/O list, see erl_iolist_to_binary.
238 ETERM *erl_iolist_to_binary(term)
240 Types:
242 ETERM *list;
244 Converts an I/O list to a binary term.
246 list is an Erlang term containing a list.
248 Returns an Erlang binary term, or NULL if list was not an I/O
250 list.
251 Informally, an I/O list is a deep list of characters and bina‐
253 ries that can be sent to an Erlang port. In BNF, an I/O list is
254 formally defined as follows:
255 iolist ::= []
257 | Binary
258 | [iohead | iolist]
259 ;
260 iohead ::= Binary
261 | Byte (integer in the range [0..255])
262 | iolist
263 ;
264 char *erl_iolist_to_string(list)
267 Types:
269 ETERM *list;
271 Converts an I/O list to a NULL-terminated C string.
273 list is an Erlang term containing an I/O list. The I/O list must
275 not contain the integer 0, as C strings may not contain this
276 value except as a terminating marker.
277 Returns a pointer to a dynamically allocated buffer containing a
279 string. If list is not an I/O list, or if list contains the
280 integer 0, NULL is returned. It is the caller's responsibility
281 to free the allocated buffer with erl_free().
282 For the definition of an I/O list, see erl_iolist_to_binary.
284 int erl_length(list)
286 Types:
288 ETERM *list;
290 Determines the length of a proper list.
292 list is an Erlang term containing a proper list. In a proper
294 list, all tails except the last point to another list cell, and
295 the last tail points to an empty list.
296 Returns -1 if list is not a proper list.
298 ETERM *erl_mk_atom(string)
300 Types:
302 const char *string;
304 Creates an atom.
306 string is the sequence of characters that will be used to create
308 the atom.
309 Returns an Erlang term containing an atom. Notice that it is the
311 caller's responsibility to ensure that string contains a valid
312 name for an atom.
313 ERL_ATOM_PTR(atom) and ERL_ATOM_PTR_UTF8(atom) can be used to
315 retrieve the atom name (as a NULL-terminated string).
316 ERL_ATOM_SIZE(atom) and ERL_ATOM_SIZE_UTF8(atom) return the
317 length of the atom name.
318 Note:
320 The UTF-8 variants were introduced in Erlang/OTP R16 and the
321 string returned by ERL_ATOM_PTR(atom) was not NULL-terminated on
322 older releases.
323 ETERM *erl_mk_binary(bptr, size)
326 Types:
328 char *bptr;
330 int size;
331 Produces an Erlang binary object from a buffer containing a
333 sequence of bytes.
334 * bptr is a pointer to a buffer containing data to be con‐
336 verted.
337 * size indicates the length of bptr.
339 Returns an Erlang binary object.
341 ERL_BIN_PTR(bin) retrieves a pointer to the binary data.
343 ERL_BIN_SIZE(bin) retrieves the size.
344 ETERM *erl_mk_empty_list()
346 Creates and returns an empty Erlang list. Notice that NULL is
348 not used to represent an empty list; Use this function instead.
349 ETERM *erl_mk_estring(string, len)
351 Types:
353 char *string;
355 int len;
356 Creates a list from a sequence of bytes.
358 * string is a buffer containing a sequence of bytes. The buf‐
360 fer does not need to be NULL-terminated.
361 * len is the length of string.
363 Returns an Erlang list object corresponding to the character
365 sequence in string.
366 ETERM *erl_mk_float(f)
368 Types:
370 double f;
372 Creates an Erlang float.
374 f is a value to be converted to an Erlang float.
376 Returns an Erlang float object with the value specified in f or
378 NULL if f is not finite.
379 ERL_FLOAT_VALUE(t) can be used to retrieve the value from an
381 Erlang float.
382 ETERM *erl_mk_int(n)
384 Types:
386 int n;
388 Creates an Erlang integer.
390 n is a value to be converted to an Erlang integer.
392 Returns an Erlang integer object with the value specified in n.
394 ERL_INT_VALUE(t) can be used to retrieve the value from an
396 Erlang integer.
397 ETERM *erl_mk_list(array, arrsize)
399 Types:
401 ETERM **array;
403 int arrsize;
404 Creates an Erlang list from an array of Erlang terms, such that
406 each element in the list corresponds to one element in the
407 array.
408 * array is an array of Erlang terms.
410 * arrsize is the number of elements in array.
412 The function creates an Erlang list object, whose length arrsize
414 and whose elements are taken from the terms in array.
415 ETERM *erl_mk_long_ref(node, n1, n2, n3, creation)
417 Types:
419 const char *node;
421 unsigned int n1, n2, n3;
422 unsigned int creation;
423 Creates an Erlang reference, with 82 bits.
425 * node is the name of the C-node.
427 * n1, n2, and n3 can be seen as one big number
429 n1*2^64+n2*2^32+n3, which is to be chosen uniquely for each
430 reference created for a given C-node.
431 * creation is an arbitrary number.
433 Notice that n3 and creation are limited in precision, so only
435 the low 18 and 2 bits of these numbers are used.
436 Returns an Erlang reference object.
438 ERL_REF_NODE(ref), ERL_REF_NUMBERS(ref), ERL_REF_LEN(ref), and
440 ERL_REF_CREATION(ref) can be used to retrieve the values used to
441 create the reference.
442 ETERM *erl_mk_pid(node, number, serial, creation)
444 Types:
446 const char *node;
448 unsigned int number;
449 unsigned int serial;
450 unsigned int creation;
451 Creates an Erlang process identifier (pid). The resulting pid
453 can be used by Erlang processes wishing to communicate with the
454 C-node.
455 * node is the name of the C-node.
457 * number, serial, and creation are arbitrary numbers. Notice
459 that these are limited in precision, so only the low 15, 3,
460 and 2 bits of these numbers are used.
461 Returns an Erlang pid object.
463 ERL_PID_NODE(pid), ERL_PID_NUMBER(pid), ERL_PID_SERIAL(pid), and
465 ERL_PID_CREATION(pid) can be used to retrieve the four values
466 used to create the pid.
467 ETERM *erl_mk_port(node, number, creation)
469 Types:
471 const char *node;
473 unsigned int number;
474 unsigned int creation;
475 Creates an Erlang port identifier.
477 * node is the name of the C-node.
479 * number and creation are arbitrary numbers. Notice that these
481 are limited in precision, so only the low 18 and 2 bits of
482 these numbers are used.
483 Returns an Erlang port object.
485 ERL_PORT_NODE(port), ERL_PORT_NUMBER(port), and ERL_PORT_CRE‐
487 ATION can be used to retrieve the three values used to create
488 the port.
489 ETERM *erl_mk_ref(node, number, creation)
491 Types:
493 const char *node;
495 unsigned int number;
496 unsigned int creation;
497 Creates an old Erlang reference, with only 18 bits - use
499 erl_mk_long_ref instead.
500 * node is the name of the C-node.
502 * number is to be chosen uniquely for each reference created
504 for a given C-node.
505 * creation is an arbitrary number.
507 Notice that number and creation are limited in precision, so
509 only the low 18 and 2 bits of these numbers are used.
510 Returns an Erlang reference object.
512 ERL_REF_NODE(ref), ERL_REF_NUMBER(ref), and ERL_REF_CRE‐
514 ATION(ref) can be used to retrieve the three values used to cre‐
515 ate the reference.
516 ETERM *erl_mk_string(string)
518 Types:
520 char *string;
522 Creates a list from a NULL-terminated string.
524 string is a NULL-terminated sequence of characters (that is, a C
526 string) from which the list will be created.
527 Returns an Erlang list.
529 ETERM *erl_mk_tuple(array, arrsize)
531 Types:
533 ETERM **array;
535 int arrsize;
536 Creates an Erlang tuple from an array of Erlang terms.
538 * array is an array of Erlang terms.
540 * arrsize is the number of elements in array.
542 The function creates an Erlang tuple, whose arity is size and
544 whose elements are taken from the terms in array.
545 To retrieve the size of a tuple, either use function erl_size
547 (which checks the type of the checked term and works for a
548 binary as well as for a tuple) or ERL_TUPLE_SIZE(tuple) returns
549 the arity of a tuple. erl_size() does the same thing, but it
550 checks that the argument is a tuple. erl_element(index,tuple)
551 returns the element corresponding to a given position in the
552 tuple.
553 ETERM *erl_mk_uint(n)
555 Types:
557 unsigned int n;
559 Creates an Erlang unsigned integer.
561 n is a value to be converted to an Erlang unsigned integer.
563 Returns an Erlang unsigned integer object with the value speci‐
565 fied in n.
566 ERL_INT_UVALUE(t) can be used to retrieve the value from an
568 Erlang unsigned integer.
569 ETERM *erl_mk_var(name)
571 Types:
573 char *name;
575 Creates an unbound Erlang variable. The variable can later be
577 bound through pattern matching or assignment.
578 name specifies a name for the variable.
580 Returns an Erlang variable object with the name name.
582 int erl_print_term(stream, term)
584 Types:
586 FILE *stream;
588 ETERM *term;
589 Prints the specified Erlang term to the specified output stream.
591 * stream indicates where the function is to send its output.
593 * term is the Erlang term to print.
595 Returns the number of characters written on success, otherwise a
597 negative value.
598 void erl_set_compat_rel(release_number)
600 Types:
602 unsigned release_number;
604 By default, the Erl_Interface library is only guaranteed to be
606 compatible with other Erlang/OTP components from the same
607 release as the Erl_Interface library itself. For example,
608 Erl_Interface from Erlang/OTP R10 is not compatible with an
609 Erlang emulator from Erlang/OTP R9 by default.
610 A call to erl_set_compat_rel(release_number) sets the Erl_Inter‐
612 face library in compatibility mode of release release_number.
613 Valid range of release_number is [7, current release]. This
614 makes it possible to communicate with Erlang/OTP components from
615 earlier releases.
616 Note:
618 If this function is called, it may only be called once directly
619 after the call to function erl_init().
620 Warning:
623 You may run into trouble if this feature is used carelessly.
624 Always ensure that all communicating components are either from
625 the same Erlang/OTP release, or from release X and release Y
626 where all components from release Y are in compatibility mode of
627 release X.
628 int erl_size(term)
631 Types:
633 ETERM *term;
635 Returns either the arity of an Erlang tuple or the number of
637 bytes in an Erlang binary object.
638 term is an Erlang tuple or an Erlang binary object.
640 Returns the size of term as described above, or -1 if term is
642 not one of the two supported types.
643 ETERM *erl_tl(list)
645 Types:
647 ETERM *list;
649 Extracts the tail from a list.
651 list is an Erlang term containing a list.
653 Returns an Erlang list corresponding to the original list minus
655 the first element, or NULL pointer if list was not a list.
656 ETERM *erl_var_content(term, name)
658 Types:
660 ETERM *term;
662 char *name;
663 Returns the contents of the specified variable in an Erlang
665 term.
666 * term is an Erlang term. In order for this function to suc‐
668 ceed, term must either be an Erlang variable with the speci‐
669 fied name, or it must be an Erlang list or tuple containing
670 a variable with the specified name. Other Erlang types can‐
671 not contain variables.
672 * name is the name of an Erlang variable.
674 Returns the Erlang object corresponding to the value of name in
676 term. If no variable with the name name is found in term, or if
677 term is not a valid Erlang term, NULL is returned.
678Ericsson AB erl_interface 3.10.2.2 erl_eterm(3)