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Tcl_SetResult(3)	    Tcl Library Procedures	      Tcl_SetResult(3)

______________________________________________________________________________

NAME
       Tcl_SetObjResult, Tcl_GetObjResult, Tcl_SetResult, Tcl_GetStringResult,
       Tcl_AppendResult, Tcl_AppendResultVA,  Tcl_AppendElement,  Tcl_ResetRe‐
       sult, 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 existing  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	inter‐
       preter 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 reference count is incremented
       since there is now a new reference to it from  interp.	The  reference
       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_IncrRef‐
       Count  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 argu‐
       ment 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  informa‐
       tion.   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 ini‐
       tialized empty state (e.g. a command  procedure	was  just  invoked  or
       Tcl_ResetResult was just called), then Tcl_AppendResult sets the result
       to the concatenation 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 management issues	 asso‐
       ciated  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-compatability 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 variable 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 cur‐
       rent result as a proper Tcl list element.  Tcl_AppendElement adds back‐
       slashes 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 ele‐
       ment.  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.	  How‐
       ever  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	associated  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 procedure  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_Get‐
       StringResult, and write the result using Tcl_SetObjResult or Tcl_SetRe‐
       sult.

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 applications 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, inter‐
       preter

Tcl				      8.0		      Tcl_SetResult(3)
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