plucky (3) Tcl_GetStringResult.3tcl.gz

Provided by: tcl9.0-doc_9.0.1+dfsg-1_all bug

NAME

       Tcl_SetObjResult,     Tcl_GetObjResult,     Tcl_SetResult,     Tcl_GetStringResult,     Tcl_AppendResult,
       Tcl_AppendElement, Tcl_ResetResult, Tcl_TransferResult - 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_ResetResult(interp)

       Tcl_TransferResult(sourceInterp, code, targetInterp)

       Tcl_AppendElement(interp, element)

ARGUMENTS

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

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

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

       const 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.

       Tcl_Interp *sourceInterp (in)           Interpreter   that  the  result  and  return  options  should  be
                                               transferred from.

       Tcl_Interp *targetInterp (in)           Interpreter  that  the  result  and  return  options  should   be
                                               transferred to.

       int code (in)                           Return code value that controls transfer of return options.
________________________________________________________________________________________________________________

DESCRIPTION

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

       Tcl_SetObjResult  arranges  for  objPtr  to be the result for interp, replacing any existing result.  The
       result is left pointing to the value 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 value is
       decremented and the old result value is freed if no references to it remain.

       Tcl_GetObjResult returns the result  for  interp  as  a  value.   The  value's  reference  count  is  not
       incremented;  if  the  caller  needs  to  retain  a  long-term  pointer  to  the  value  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  a  value  by  a
       Tcl_SetObjResult  call, the value form will be converted to a string and returned.  If the value'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 value 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  a  value,  its  reference count is decremented and the result is left pointing to an
       unshared value 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 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 (char *)NULL.

       Tcl_TransferResult transfers interpreter state from sourceInterp to targetInterp.  The  two  interpreters
       must  have  been  created  in the same thread.  If sourceInterp and targetInterp are the same, nothing is
       done. Otherwise, Tcl_TransferResult moves the result from sourceInterp to targetInterp,  and  resets  the
       result  in  sourceInterp.  It  also  moves the return options dictionary as controlled by the return code
       value code in the same manner as Tcl_GetReturnOptions.

DEPRECATED INTERFACES

   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 a value 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.

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(
                      void *blockPtr);

       When freeProc is called, its blockPtr will be set to the value of result passed to Tcl_SetResult.

REFERENCE COUNT MANAGEMENT

       The interpreter result is one of the main places that owns references to values, along with the  bytecode
       execution stack, argument lists, variables, and the list and dictionary collection values.

       Tcl_SetObjResult  takes  a  value  with  an  arbitrary  reference count (specifically including zero) and
       guarantees to increment the reference count. If code wishes to continue using the value after setting  it
       as the result, it should add its own reference to it with Tcl_IncrRefCount.

       Tcl_GetObjResult  returns  the  current  interpreter result value. This will have a reference count of at
       least 1. If the caller wishes to keep the interpreter result value, it  should  increment  its  reference
       count.

       Tcl_GetStringResult  does not manipulate reference counts, but the string it returns is owned by (and has
       a lifetime controlled by) the current interpreter result value; it should  be  copied  instead  of  being
       relied  upon  to  persist  after the next Tcl API call, as most Tcl operations can modify the interpreter
       result.

       Tcl_SetResult, Tcl_AppendResult,  Tcl_AppendElement,  and  Tcl_ResetResult  all  modify  the  interpreter
       result.  They  may  cause  the  old  interpreter result to have its reference count decremented and a new
       interpreter result to be allocated. After they have been called, the reference count of  the  interpreter
       result is guaranteed to be 1.

SEE ALSO

       Tcl_AddErrorInfo, Tcl_CreateObjCommand, Tcl_SetErrorCode, Tcl_Interp, Tcl_GetReturnOptions

KEYWORDS

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