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Tcl_SetResult(3)		      Tcl Library Procedures			 Tcl_SetResult(3)

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NAME
       Tcl_SetObjResult,  Tcl_GetObjResult, Tcl_SetResult, Tcl_GetStringResult, Tcl_AppendResult,
       Tcl_AppendResultVA, Tcl_AppendElement, Tcl_ResetResult, Tcl_FreeResult  -  manipulate  Tcl
       result

SYNOPSIS
       #include <tcl.h>

       Tcl_SetObjResult(interp, objPtr)

       Tcl_Obj *
       Tcl_GetObjResult(interp)

       Tcl_SetResult(interp, result, freeProc)

       const char *
       Tcl_GetStringResult(interp)

       Tcl_AppendResult(interp, result, result, ... , (char *) NULL)

       Tcl_AppendResultVA(interp, argList)

       Tcl_AppendElement(interp, element)

       Tcl_ResetResult(interp)

       Tcl_FreeResult(interp)

ARGUMENTS
       Tcl_Interp *interp (out) 	   Interpreter whose result is to be modified or read.

       Tcl_Obj *objPtr (in)		   Object value to become result for interp.

       char *result (in)		   String  value  to  become  result  for interp or to be
					   appended to the existing result.

       char *element (in)		   String value to append as a list element to the exist-
					   ing result of interp.

       Tcl_FreeProc *freeProc (in)	   Address  of	procedure  to  call to release storage at
					   result, or TCL_STATIC, TCL_DYNAMIC, or TCL_VOLATILE.

       va_list argList (in)		   An argument list  which  must  have	been  initialized
					   using va_start, and cleared using va_end.
_________________________________________________________________

DESCRIPTION
       The  procedures	described  here  are utilities for manipulating the result value in a Tcl
       interpreter.  The interpreter result may be either a Tcl object or a string.  For example,
       Tcl_SetObjResult  and Tcl_SetResult set the interpreter result to, respectively, an object
       and a string.  Similarly, Tcl_GetObjResult and Tcl_GetStringResult return the  interpreter
       result  as  an  object  and as a string.  The procedures always keep the string and object
       forms of the interpreter result consistent.  For example, if Tcl_SetObjResult is called to
       set  the  result  to  an  object,  then	Tcl_GetStringResult is called, it will return the
       object's string value.

       Tcl_SetObjResult arranges for objPtr to be the result for interp, replacing  any  existing
       result.	 The result is left pointing to the object referenced by objPtr.  objPtr's refer-
       ence count is incremented since there is now a new reference to it from interp.	The  ref-
       erence  count  for any old result object is decremented and the old result object is freed
       if no references to it remain.

       Tcl_GetObjResult returns the result for interp as an object.  The object's reference count
       is  not	incremented; if the caller needs to retain a long-term pointer to the object they
       should use Tcl_IncrRefCount to increment its reference count in	order  to  keep  it  from
       being freed too early or accidentally changed.

       Tcl_SetResult  arranges for result to be the result for the current Tcl command in interp,
       replacing any existing result.  The freeProc argument specifies how to manage the  storage
       for  the  result  argument;  it	is  discussed in the section THE TCL_FREEPROC ARGUMENT TO
       TCL_SETRESULT below.  If result is NULL, then freeProc is ignored  and  Tcl_SetResult  re-
       initializes interp's result to point to an empty string.

       Tcl_GetStringResult  returns  the result for interp as a string.  If the result was set to
       an object by a Tcl_SetObjResult call, the object form will be converted to  a  string  and
       returned.  If the object's string representation contains null bytes, this conversion will
       lose information.  For this reason, programmers are encouraged to write their code to  use
       the new object API procedures and to call Tcl_GetObjResult instead.

       Tcl_ResetResult	clears	the  result  for interp and leaves the result in its normal empty
       initialized state.  If the result is an object, its reference count is decremented and the
       result is left pointing to an unshared object representing an empty string.  If the result
       is a dynamically allocated string, its memory is free*d and the result is left as a  empty
       string.	 Tcl_ResetResult  also	clears	the  error  state  managed  by	Tcl_AddErrorInfo,
       Tcl_AddObjErrorInfo, and Tcl_SetErrorCode.

       Tcl_AppendResult makes it easy to build up Tcl results in pieces.  It takes  each  of  its
       result  arguments  and appends them in order to the current result associated with interp.
       If the result is in its initialized empty state (e.g. a command procedure was just invoked
       or Tcl_ResetResult was just called), then Tcl_AppendResult sets the result to the concate-
       nation of its result arguments.	Tcl_AppendResult may be called repeatedly  as  additional
       pieces of the result are produced.  Tcl_AppendResult takes care of all the storage manage-
       ment issues associated with managing interp's result, such as allocating a  larger  result
       area  if necessary.  It also manages conversion to and from the result field of the interp
       so as to handle backward-compatibility with old-style extensions.  Any  number  of  result
       arguments  may  be  passed  in a single call; the last argument in the list must be a NULL
       pointer.

       Tcl_AppendResultVA is the same as Tcl_AppendResult except that instead of taking  a  vari-
       able number of arguments it takes an argument list.

OLD STRING PROCEDURES
       Use  of	the following procedures (is deprecated since they manipulate the Tcl result as a
       string.	Procedures such as Tcl_SetObjResult that manipulate the result as an  object  can
       be significantly more efficient.

       Tcl_AppendElement  is similar to Tcl_AppendResult in that it allows results to be built up
       in pieces.  However, Tcl_AppendElement takes only a single element argument and it appends
       that  argument to the current result as a proper Tcl list element.  Tcl_AppendElement adds
       backslashes or braces if necessary to ensure that interp's result can be parsed as a  list
       and  that  element  will  be  extracted	as  a  single  element.  Under normal conditions,
       Tcl_AppendElement will add a space character to interp's result just before adding the new
       list  element, so that the list elements in the result are properly separated.  However if
       the new list element is the first in a list or sub-list (i.e. interp's current  result  is
       empty,  or  consists  of the single character "{", or ends in the characters " {") then no
       space is added.

       Tcl_FreeResult performs part of the work of Tcl_ResetResult.  It frees up the memory asso-
       ciated  with  interp's result.  It also sets interp->freeProc to zero, but does not change
       interp->result or clear error state.  Tcl_FreeResult is most commonly used when	a  proce-
       dure is about to replace one result value with another.

DIRECT ACCESS TO INTERP->;RESULT IS DEPRECATED
       It  used  to be legal for programs to directly read and write interp->result to manipulate
       the interpreter result.	Direct	access	to  interp->result  is	now  strongly  deprecated
       because	it  can  make the result's string and object forms inconsistent.  Programs should
       always read the result using the procedures Tcl_GetObjResult or	Tcl_GetStringResult,  and
       write the result using Tcl_SetObjResult or Tcl_SetResult.

THE TCL_FREEPROC ARGUMENT TO TCL_SETRESULT
       Tcl_SetResult's	freeProc  argument  specifies how the Tcl system is to manage the storage
       for the result argument.  If Tcl_SetResult or Tcl_SetObjResult are called at a  time  when
       interp  holds  a string result, they do whatever is necessary to dispose of the old string
       result (see the Tcl_Interp manual entry for details on this).

       If freeProc is TCL_STATIC it means that result refers to an area of static storage that is
       guaranteed  not	to  be modified until at least the next call to Tcl_Eval.  If freeProc is
       TCL_DYNAMIC it means that result was allocated with a call to Tcl_Alloc	and  is  now  the
       property  of  the  Tcl  system.	Tcl_SetResult will arrange for the string's storage to be
       released by calling Tcl_Free when it is no longer needed.  If freeProc is TCL_VOLATILE  it
       means  that  result  points  to	an  area  of memory that is likely to be overwritten when
       Tcl_SetResult returns (e.g. it points to something  in  a  stack  frame).   In  this  case
       Tcl_SetResult  will make a copy of the string in dynamically allocated storage and arrange
       for the copy to be the result for the current Tcl command.

       If freeProc is not one of the values TCL_STATIC, TCL_DYNAMIC, and TCL_VOLATILE, then it is
       the  address of a procedure that Tcl should call to free the string.  This allows applica-
       tions to use non-standard storage allocators.  When Tcl no longer needs	the  storage  for
       the  string,  it  will call freeProc. FreeProc should have arguments and result that match
       the type Tcl_FreeProc:
	      typedef void Tcl_FreeProc(char *blockPtr);
       When freeProc is called, its blockPtr will be  set  to  the  value  of  result  passed  to
       Tcl_SetResult.

SEE ALSO
       Tcl_AddErrorInfo, Tcl_CreateObjCommand, Tcl_SetErrorCode, Tcl_Interp

KEYWORDS
       append, command, element, list, object, result, return value, interpreter

Tcl					       8.0				 Tcl_SetResult(3)
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