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erl_eterm(3erl) | C Library Functions | erl_eterm(3erl) |
NAME¶
erl_eterm - Functions for Erlang Term ConstructionDESCRIPTION¶
This module contains 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, because it may be changed in future releases to provide faster and more compact term storage. Instead, applications should us the macros and functions provided. The following macros each take a single ETERM pointer as an argument. They return a non-zero value if the test is true, and 0 otherwise:- ERL_IS_INTEGER(t):
- True if t is an integer.
- ERL_IS_UNSIGNED_INTEGER(t):
- True if t is an integer.
- ERL_IS_FLOAT(t):
- True if t is a floating point number.
- ERL_IS_ATOM(t):
- True if t is an atom.
- ERL_IS_PID(t):
- True if t is a Pid (process identifier).
- ERL_IS_PORT(t):
- True if t is a port.
- ERL_IS_REF(t):
- True if t is a reference.
- ERL_IS_TUPLE(t):
- True if t is a tuple.
- ERL_IS_BINARY(t):
- True if t is a binary.
- ERL_IS_LIST(t):
- True if t is a list with zero or more elements.
- ERL_IS_EMPTY_LIST(t):
- True if t is an empty list.
- ERL_IS_CONS(t):
- True if t is a list with at least one element.
- char *ERL_ATOM_PTR(t):
- char *ERL_ATOM_PTR_UTF8(t):
- A string representing atom t.
- int ERL_ATOM_SIZE(t):
- int ERL_ATOM_SIZE_UTF8(t):
- The length (in bytes) of atom t.
- void *ERL_BIN_PTR(t):
- A pointer to the contents of t
- int ERL_BIN_SIZE(t):
- The length (in bytes) of binary object t.
- int ERL_INT_VALUE(t):
- The integer of t.
- unsigned int ERL_INT_UVALUE(t):
- The unsigned integer value of t.
- double ERL_FLOAT_VALUE(t):
- The floating point value of t.
- ETERM *ERL_PID_NODE(t):
- ETERM *ERL_PID_NODE_UTF8(t):
- The Node in pid t.
- int ERL_PID_NUMBER(t):
- The sequence number in pid t.
- int ERL_PID_SERIAL(t):
- The serial number in pid t.
- int ERL_PID_CREATION(t):
- The creation number in pid t.
- int ERL_PORT_NUMBER(t):
- The sequence number in port t.
- int ERL_PORT_CREATION(t):
- The creation number in port t.
- ETERM *ERL_PORT_NODE(t):
- ETERM *ERL_PORT_NODE_UTF8(t):
- The node in port t.
- int ERL_REF_NUMBER(t):
- The first part of the reference number in ref t. Use only for compatibility.
- int ERL_REF_NUMBERS(t):
- Pointer to the array of reference numbers in ref t.
- int ERL_REF_LEN(t):
- The number of used reference numbers in ref t.
- int ERL_REF_CREATION(t):
- The creation number in ref t.
- int ERL_TUPLE_SIZE(t):
- The number of elements in tuple t.
- ETERM *ERL_CONS_HEAD(t):
- The head element of list t.
- ETERM *ERL_CONS_TAIL(t):
- A List representing the tail elements of list t.
EXPORTS¶
ETERM *erl_cons(head, tail)
Types:
ETERM *head;
ETERM *tail;
This function concatenates two Erlang terms, prepending head onto
tail and thereby creating a cons cell. To make a proper list,
tail should always be a list or an empty list. Note that NULL is not a
valid list.
head is the new term to be added.
tail is the existing list to which head will be 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) will do the same thing, but check that the argument really
is a list.
For example:
ETERM *erl_copy_term(term)
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);
Types:
ETERM *term;
This function creates and returns a copy of the Erlang term term.
ETERM *erl_element(position, tuple)
Types:
int position;
ETERM *tuple;
This function 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.
The function returns a new Erlang term corresponding to the requested element,
or NULL if position was greater than the arity of tuple.
void erl_init(NULL, 0)
Types:
void *NULL;
int 0;
This function must be called before any of the others in the
erl_interface library in order to initialize the library functions. The
arguments must be specified as erl_init(NULL,0).
ETERM *erl_hd(list)
Types:
ETERM *list;
Extracts the first element from a list.
list is an Erlang term containing a list.
The function returns an Erlang term corresponding to the head element in the
list, or a NULL pointer if list was not a list.
ETERM *erl_iolist_to_binary(term)
Types:
ETERM *list;
This function converts an IO list to a binary term.
list is an Erlang term containing a list.
This function an Erlang binary term, or NULL if list was not an IO list.
Informally, an IO list is a deep list of characters and binaries which can be
sent to an Erlang port. In BNF, an IO list is formally defined as follows:
char *erl_iolist_to_string(list)
iolist ::= [] | Binary | [iohead | iolist] ; iohead ::= Binary | Byte (integer in the range [0..255]) | iolist ;
Types:
ETERM *list;
This function converts an IO list to a '\0' terminated C string.
list is an Erlang term containing an IO list. The IO list must not
contain the integer 0, since C strings may not contain this value except as a
terminating marker.
This function returns a pointer to a dynamically allocated buffer containing a
string. If list is not an IO list, or if list contains the
integer 0, NULL is returned. It is the caller's responsibility free the
allocated buffer with erl_free().
Refer to erl_iolist_to_binary() for the definition of an IO list.
int erl_iolist_length(list)
Types:
ETERM *list;
Returns the length of an IO list.
list is an Erlang term containing an IO list.
The function returns the length of list, or -1 if list is not an
IO list.
Refer to erl_iolist_to_binary() for the definition of an IO list.
int erl_length(list)
Types:
ETERM *list;
Determines the length of a proper list.
list is an Erlang term containing 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)
Types:
const char *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. Note that it is the callers
responsibility to make sure 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) returns the
length of the atom name.
ETERM *erl_mk_binary(bptr, size)
Note:
Note that the UTF8 variants were introduced in Erlang/OTP releases R16 and the
string returned by ERL_ATOM_PTR(atom) was not null terminated on older
releases.
Types:
char *bptr;
int size;
This function 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.
The function 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()
This function creates and returns an empty Erlang list. Note that NULL is not
used to represent an empty list; Use this function instead.
ETERM *erl_mk_estring(string, len)
Types:
char *string;
int len;
This function creates a list from a sequence of bytes.
string is a buffer containing a sequence of bytes. The buffer does not
need to be zero-terminated.
len is the length of string.
The function returns an Erlang list object corresponding to the character
sequence in string.
ETERM *erl_mk_float(f)
Types:
double f;
Creates an Erlang float.
f is a value to be converted to an Erlang float.
The function returns an Erlang float object with the value specified in
f.
ERL_FLOAT_VALUE(t) can be used to retrieve the value from an Erlang
float.
ETERM *erl_mk_int(n)
Types:
int n;
Creates an Erlang integer.
n is a value to be converted to an Erlang integer.
The function returns an Erlang integer object with the value specified in
n.
ERL_INT_VALUE(t) can be used to retrieve the value value from an Erlang
integer.
ETERM *erl_mk_list(array, arrsize)
Types:
ETERM **array;
int 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_pid(node, number, serial, creation)
Types:
const char *node;
unsigned int number;
unsigned int serial;
unsigned int creation;
This function creates an Erlang process identifier. 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. Note
though, that these are limited in precision, so only the low 15, 3 and 2 bits
of these numbers are actually used.
The function 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)
Types:
const char *node;
unsigned int number;
unsigned int creation;
This function creates an Erlang port identifier.
node is the name of the C node.
number and creation are arbitrary numbers. Note though, that these
are limited in precision, so only the low 18 and 2 bits of these numbers are
actually used.
The function 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)
Types:
const char *node;
unsigned int number;
unsigned int creation;
This function creates an old Erlang reference, with only 18 bits - use
erl_mk_long_ref instead.
node is the name of the C node.
number should be chosen uniquely for each reference created for a given C
node.
creation is an arbitrary number.
Note that number and creation are limited in precision, so only
the low 18 and 2 bits of these numbers are actually used.
The function returns an Erlang reference object.
ERL_REF_NODE(ref), ERL_REF_NUMBER(ref), and
ERL_REF_CREATION(ref) to retrieve the three values used to create the
reference.
ETERM *erl_mk_long_ref(node, n1, n2, n3, creation)
Types:
const char *node;
unsigned int n1, n2, n3;
unsigned int creation;
This function 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 should be chosen uniquely for each reference
created for a given C node.
creation is an arbitrary number.
Note that n3 and creation are limited in precision, so only the
low 18 and 2 bits of these numbers are actually used.
The function returns an Erlang reference object.
ERL_REF_NODE(ref), ERL_REF_NUMBERS(ref), ERL_REF_LEN(ref)
and ERL_REF_CREATION(ref) to retrieve the values used to create the
reference.
ETERM *erl_mk_string(string)
Types:
char *string;
This function creates a list from a zero terminated string.
string is the zero-terminated sequence of characters (i.e. a C string)
from which the list will be created.
The function returns an Erlang list.
ETERM *erl_mk_tuple(array, arrsize)
Types:
ETERM **array;
int 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 the erl_size function (which
checks the type of the checked term and works for a binary as well as for a
tuple), or the ERL_TUPLE_SIZE(tuple) returns the arity of a tuple.
erl_size() will do the same thing, but it checks that the argument
really is a tuple. erl_element(index,tuple) returns the element
corresponding to a given position in the tuple.
ETERM *erl_mk_uint(n)
Types:
unsigned int n;
Creates an Erlang unsigned integer.
n is a value to be converted to an Erlang unsigned integer.
The function 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)
Types:
char *name;
This function creates an unbound Erlang variable. The variable can later be
bound through pattern matching or assignment.
name specifies a name for the variable.
The function returns an Erlang variable object with the name name.
int erl_print_term(stream, term)
Types:
FILE *stream;
ETERM *term;
This function prints the specified Erlang term to the given output stream.
stream indicates where the function should send its output.
term is the Erlang term to print.
The function returns the number of characters written, or a negative value if
there was an error.
void erl_set_compat_rel(release_number)
Types:
unsigned 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
the OTP R10 release is not compatible with an Erlang emulator from the OTP R9
release 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.
int erl_size(term)
Note:
If this function is called, it may only be called once directly after the call
to the erl_init() function.
Warning:
You may run into trouble if this feature is used carelessly. Always make sure
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.
Types:
ETERM *term;
Returns 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.
The function returns the size of term as described above, or -1 if
term is not one of the two supported types.
ETERM *erl_tl(list)
Types:
ETERM *list;
Extracts the tail from a list.
list is an Erlang term containing a list.
The function 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)
Types:
ETERM *term;
char *name;
This function 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 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 was found in
term, or if term is not a valid Erlang term, NULL is
returned.
erl_interface 3.7.18 | Ericsson AB |