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Linux 2.6 - man page for erl_eterm (linux section 3erl)

erl_eterm(3erl) 		       C Library Functions			  erl_eterm(3erl)

NAME
       erl_eterm - Functions for Erlang Term Construction

DESCRIPTION
       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.

       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() will likely result in garbage.

	 char *ERL_ATOM_PTR(t) :
	   A string representing atom t .

	 int ERL_ATOM_SIZE(t) :
	   The length (in characters) 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) :
	   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) :
	   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 *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)

	      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:

	      iolist ::= []
		      |   Binary
		      |   [iohead | iolist]
		      ;
	      iohead ::= Binary
		      |   Byte (integer in the range [0..255])
		      |   iolist
		      ;

       char * erl_iolist_to_string(list)

	      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  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 responsibil-
	      ity to make sure that string contains a valid name for an atom.

	      ERL_ATOM_PTR(atom) can be used to retrieve the atom name (as a string).  Note  that
	      the  string is not 0-terminated in the atom. ERL_ATOM_SIZE(atom) returns the length
	      of the atom name.

       ETERM * erl_mk_binary(bptr, size)

	      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 actu-
	      ally used.

	      The function returns an Erlang pid object.

	      ERL_PID_NODE(pid) ,  ERL_PID_NUMBER(pid)	,  ERL_PID_SERIAL(pid)	and  ERL_PID_CRE-
	      ATION(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_CRE-
	      ATION(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  inte-
	      ger.

       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 com-
	      patibility  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.

   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.

       int erl_size(term)

	      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 con-
	      taining a variable with the specified name. Other Erlang types cannot contain vari-
	      ables.

	      name is the name of an Erlang variable.

	      Returns the Erlang object corresponding to the value of name in term . If no  vari-
	      able  with the name name was found in term , or if term is not a valid Erlang term,
	      NULL is returned.

Ericsson AB			       erl_interface 3.7.3			  erl_eterm(3erl)


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