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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_Appen-dResultVA, Tcl_AppendResultVA,
       dResultVA, 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 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 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 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_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 argu-ment; argument;
       ment; 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 point-ing pointing
       ing 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  argu-ments arguments
       ments  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  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 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 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
       current result as a proper Tcl list element.  Tcl_AppendElement adds backslashes or braces if  neces-sary necessary
       sary  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 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 inter-preter interpreter
       preter 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 pro-cedures procedures
       cedures 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 applications to use non-standard nonstandard
       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)