The UTF-8 variants were introduced in Erlang/OTP R16 and the string returned by ERL_ATOM_PTR(atom)
was not NULL
-terminated on older releases.
erl_eterm
Functions for Erlang term construction.
This module provides functions for creating and manipulating Erlang terms.
An Erlang term is represented by a C structure of type ETERM
. Applications should not reference any fields in this structure directly, as it can be changed in future releases to provide faster and more compact term storage. Instead, applications should use the macros and functions provided.
Each of the following macros takes a single ETERM
pointer as an argument. The macros return a non-zero value if the test is true, otherwise 0
.
ERL_IS_INTEGER(t)
t
is an integer.ERL_IS_UNSIGNED_INTEGER(t)
t
is an integer.ERL_IS_FLOAT(t)
t
is a floating point number.ERL_IS_ATOM(t)
t
is an atom.ERL_IS_PID(t)
t
is a pid (process identifier).ERL_IS_PORT(t)
t
is a port.ERL_IS_REF(t)
t
is a reference.ERL_IS_TUPLE(t)
t
is a tuple.ERL_IS_BINARY(t)
t
is a binary.ERL_IS_LIST(t)
t
is a list with zero or more elements.ERL_IS_EMPTY_LIST(t)
t
is an empty list.ERL_IS_CONS(t)
t
is a list with at least one element.The following macros can be used for retrieving parts of Erlang terms. None of these do any type checking. Results are undefined if you pass an ETERM*
containing the wrong type. For example, passing a tuple to ERL_ATOM_PTR()
likely results in garbage.
char *ERL_ATOM_PTR(t)
char *ERL_ATOM_PTR_UTF8(t)
t
.int ERL_ATOM_SIZE(t)
int ERL_ATOM_SIZE_UTF8(t)
t
.void *ERL_BIN_PTR(t)
t
.int ERL_BIN_SIZE(t)
t
.int ERL_INT_VALUE(t)
t
.unsigned int ERL_INT_UVALUE(t)
t
.double ERL_FLOAT_VALUE(t)
t
.ETERM *ERL_PID_NODE(t)
ETERM *ERL_PID_NODE_UTF8(t)
t
.int ERL_PID_NUMBER(t)
t
.int ERL_PID_SERIAL(t)
t
.int ERL_PID_CREATION(t)
t
.int ERL_PORT_NUMBER(t)
t
.int ERL_PORT_CREATION(t)
t
.ETERM *ERL_PORT_NODE(t)
ETERM *ERL_PORT_NODE_UTF8(t)
t
.int ERL_REF_NUMBER(t)
t
. Use only for compatibility.int ERL_REF_NUMBERS(t)
t
.int ERL_REF_LEN(t)
t
.int ERL_REF_CREATION(t)
t
.int ERL_TUPLE_SIZE(t)
t
.ETERM *ERL_CONS_HEAD(t)
t
.ETERM *ERL_CONS_TAIL(t)
t
.ETERM *erl_cons(head, tail)
Concatenates two Erlang terms, prepending head
onto tail
and thereby creating a cons
cell. To make a proper list, tail
is always to be a list or an empty list. Notice that NULL
is not a valid list.
head
is the new term to be added.tail
is the existing list to which head
is concatenated.The function returns a new list.
ERL_CONS_HEAD(list)
and ERL_CONS_TAIL(list)
can be used to retrieve the head and tail components from the list. erl_hd(list)
and erl_tl(list)
do the same thing, but check that the argument really is a list.
Example:
ETERM *list,*anAtom,*anInt; anAtom = erl_mk_atom("madonna"); anInt = erl_mk_int(21); list = erl_mk_empty_list(); list = erl_cons(anAtom, list); list = erl_cons(anInt, list); ... /* do some work */ erl_free_compound(list);
ETERM *erl_copy_term(term)
Creates and returns a copy of the Erlang term term
.
ETERM *erl_element(position, tuple)
Extracts a specified element from an Erlang tuple.
position
specifies which element to retrieve from tuple
. The elements are numbered starting from 1.tuple
is an Erlang term containing at least position
elements.Returns a new Erlang term corresponding to the requested element, or NULL
if position
was greater than the arity of tuple
.
ETERM *erl_hd(list)
Extracts the first element from a list.
list
is an Erlang term containing a list.
Returns an Erlang term corresponding to the head head element in the list, or a NULL
pointer if list
was not a list.
void erl_init(NULL, 0)
This function must be called before any of the others in the Erl_Interface
library to initialize the library functions. The arguments must be specified as erl_init(NULL,0)
.
int erl_iolist_length(list)
Returns the length of an I/O list.
list
is an Erlang term containing an I/O list.
Returns the length of list
, or -1
if list
is not an I/O list.
For the definition of an I/O list, see erl_iolist_to_binary
.
ETERM *erl_iolist_to_binary(term)
Converts an I/O list to a binary term.
list
is an Erlang term containing a list.
Returns an Erlang binary term, or NULL
if list
was not an I/O list.
Informally, an I/O list is a deep list of characters and binaries that can be sent to an Erlang port. In BNF, an I/O list is formally defined as follows:
iolist ::= [] | Binary | [iohead | iolist] ; iohead ::= Binary | Byte (integer in the range [0..255]) | iolist ;
char *erl_iolist_to_string(list)
Converts an I/O list to a NULL
-terminated C string.
list
is an Erlang term containing an I/O list. The I/O list must not contain the integer 0, as C strings may not contain this value except as a terminating marker.
Returns a pointer to a dynamically allocated buffer containing a string. If list
is not an I/O list, or if list
contains the integer 0, NULL
is returned. It is the caller's responsibility to free the allocated buffer with erl_free()
.
For the definition of an I/O list, see erl_iolist_to_binary
.
int erl_length(list)
Determines the length of a proper list.
list
is an Erlang term containing a proper list. In a proper list, all tails except the last point to another list cell, and the last tail points to an empty list.
Returns -1
if list
is not a proper list.
ETERM *erl_mk_atom(string)
Creates an atom.
string
is the sequence of characters that will be used to create the atom.
Returns an Erlang term containing an atom. Notice that it is the caller's responsibility to ensure that string
contains a valid name for an atom.
ERL_ATOM_PTR(atom)
and ERL_ATOM_PTR_UTF8(atom)
can be used to retrieve the atom name (as a NULL
-terminated string). ERL_ATOM_SIZE(atom)
and ERL_ATOM_SIZE_UTF8(atom)
return the length of the atom name.
The UTF-8 variants were introduced in Erlang/OTP R16 and the string returned by ERL_ATOM_PTR(atom)
was not NULL
-terminated on older releases.
ETERM *erl_mk_binary(bptr, size)
Produces an Erlang binary object from a buffer containing a sequence of bytes.
bptr
is a pointer to a buffer containing data to be converted.size
indicates the length of bptr
.Returns an Erlang binary object.
ERL_BIN_PTR(bin)
retrieves a pointer to the binary data. ERL_BIN_SIZE(bin)
retrieves the size.
ETERM *erl_mk_empty_list()
Creates and returns an empty Erlang list. Notice that NULL
is not used to represent an empty list; Use this function instead.
ETERM *erl_mk_estring(string, len)
Creates a list from a sequence of bytes.
string
is a buffer containing a sequence of bytes. The buffer does not need to be NULL
-terminated.len
is the length of string
.Returns an Erlang list object corresponding to the character sequence in string
.
ETERM *erl_mk_float(f)
Creates an Erlang float.
f
is a value to be converted to an Erlang float.
Returns an Erlang float object with the value specified in f
or NULL
if f
is not finite.
ERL_FLOAT_VALUE(t)
can be used to retrieve the value from an Erlang float.
ETERM *erl_mk_int(n)
Creates an Erlang integer.
n
is a value to be converted to an Erlang integer.
Returns an Erlang integer object with the value specified in n
.
ERL_INT_VALUE(t)
can be used to retrieve the value from an Erlang integer.
ETERM *erl_mk_list(array, arrsize)
Creates an Erlang list from an array of Erlang terms, such that each element in the list corresponds to one element in the array.
array
is an array of Erlang terms.arrsize
is the number of elements in array
.The function creates an Erlang list object, whose length arrsize
and whose elements are taken from the terms in array
.
ETERM *erl_mk_long_ref(node, n1, n2, n3, creation)
Creates an Erlang reference, with 82 bits.
node
is the name of the C-node.n1
, n2
, and n3
can be seen as one big number n1*2^64+n2*2^32+n3
, which is to be chosen uniquely for each reference created for a given C-node.creation
is an arbitrary number.Notice that n3
and creation
are limited in precision, so only the low 18 and 2 bits of these numbers are used.
Returns an Erlang reference object.
ERL_REF_NODE(ref)
, ERL_REF_NUMBERS(ref)
, ERL_REF_LEN(ref)
, and ERL_REF_CREATION(ref)
can be used to retrieve the values used to create the reference.
ETERM *erl_mk_pid(node, number, serial, creation)
Creates an Erlang process identifier (pid). The resulting pid can be used by Erlang processes wishing to communicate with the C-node.
node
is the name of the C-node.number
, serial
, and creation
are arbitrary numbers. Notice that these are limited in precision, so only the low 15, 3, and 2 bits of these numbers are used.Returns an Erlang pid object.
ERL_PID_NODE(pid)
, ERL_PID_NUMBER(pid)
, ERL_PID_SERIAL(pid)
, and ERL_PID_CREATION(pid)
can be used to retrieve the four values used to create the pid.
ETERM *erl_mk_port(node, number, creation)
Creates an Erlang port identifier.
node
is the name of the C-node.number
and creation
are arbitrary numbers. Notice that these are limited in precision, so only the low 18 and 2 bits of these numbers are used.Returns an Erlang port object.
ERL_PORT_NODE(port)
, ERL_PORT_NUMBER(port)
, and ERL_PORT_CREATION
can be used to retrieve the three values used to create the port.
ETERM *erl_mk_ref(node, number, creation)
Creates an old Erlang reference, with only 18 bits - use erl_mk_long_ref
instead.
node
is the name of the C-node.number
is to be chosen uniquely for each reference created for a given C-node.creation
is an arbitrary number.Notice that number
and creation
are limited in precision, so only the low 18 and 2 bits of these numbers are used.
Returns an Erlang reference object.
ERL_REF_NODE(ref)
, ERL_REF_NUMBER(ref)
, and ERL_REF_CREATION(ref)
can be used to retrieve the three values used to create the reference.
ETERM *erl_mk_string(string)
Creates a list from a NULL
-terminated string.
string
is a NULL
-terminated sequence of characters (that is, a C string) from which the list will be created.
Returns an Erlang list.
ETERM *erl_mk_tuple(array, arrsize)
Creates an Erlang tuple from an array of Erlang terms.
array
is an array of Erlang terms.arrsize
is the number of elements in array
.The function creates an Erlang tuple, whose arity is size
and whose elements are taken from the terms in array
.
To retrieve the size of a tuple, either use function erl_size
(which checks the type of the checked term and works for a binary as well as for a tuple) or ERL_TUPLE_SIZE(tuple)
returns the arity of a tuple. erl_size()
does the same thing, but it checks that the argument is a tuple. erl_element(index,tuple)
returns the element corresponding to a given position in the tuple.
ETERM *erl_mk_uint(n)
Creates an Erlang unsigned integer.
n
is a value to be converted to an Erlang unsigned integer.
Returns an Erlang unsigned integer object with the value specified in n
.
ERL_INT_UVALUE(t)
can be used to retrieve the value from an Erlang unsigned integer.
ETERM *erl_mk_var(name)
Creates an unbound Erlang variable. The variable can later be bound through pattern matching or assignment.
name
specifies a name for the variable.
Returns an Erlang variable object with the name name
.
int erl_print_term(stream, term)
Prints the specified Erlang term to the specified output stream.
stream
indicates where the function is to send its output.term
is the Erlang term to print.Returns the number of characters written on success, otherwise a negative value.
void erl_set_compat_rel(release_number)
By default, the Erl_Interface
library is only guaranteed to be compatible with other Erlang/OTP components from the same release as the Erl_Interface
library itself. For example, Erl_Interface
from Erlang/OTP R10 is not compatible with an Erlang emulator from Erlang/OTP R9 by default.
A call to erl_set_compat_rel(release_number)
sets the Erl_Interface
library in compatibility mode of release release_number
. Valid range of release_number
is [7, current release]. This makes it possible to communicate with Erlang/OTP components from earlier releases.
If this function is called, it may only be called once directly after the call to function erl_init()
.
You may run into trouble if this feature is used carelessly. Always ensure that all communicating components are either from the same Erlang/OTP release, or from release X and release Y where all components from release Y are in compatibility mode of release X.
int erl_size(term)
Returns either the arity of an Erlang tuple or the number of bytes in an Erlang binary object.
term
is an Erlang tuple or an Erlang binary object.
Returns the size of term
as described above, or -1
if term
is not one of the two supported types.
ETERM *erl_tl(list)
Extracts the tail from a list.
list
is an Erlang term containing a list.
Returns an Erlang list corresponding to the original list minus the first element, or NULL
pointer if list
was not a list.
ETERM *erl_var_content(term, name)
Returns the contents of the specified variable in an Erlang term.
term
is an Erlang term. In order for this function to succeed, term
must either be an Erlang variable with the specified name, or it must be an Erlang list or tuple containing a variable with the specified name. Other Erlang types cannot contain variables.name
is the name of an Erlang variable. Returns the Erlang object corresponding to the value of name
in term
. If no variable with the name name
is found in term
, or if term
is not a valid Erlang term, NULL
is returned.
© 2010–2017 Ericsson AB
Licensed under the Apache License, Version 2.0.