1Tcl_SetResult(3)            Tcl Library Procedures            Tcl_SetResult(3)
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3
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5______________________________________________________________________________
6

NAME

8       Tcl_SetObjResult, Tcl_GetObjResult, Tcl_SetResult, Tcl_GetStringResult,
9       Tcl_AppendResult, Tcl_AppendResultVA,  Tcl_AppendElement,  Tcl_ResetRe‐
10       sult, Tcl_TransferResult, Tcl_FreeResult - manipulate Tcl result
11

SYNOPSIS

13       #include <tcl.h>
14
15       Tcl_SetObjResult(interp, objPtr)
16
17       Tcl_Obj *
18       Tcl_GetObjResult(interp)
19
20       Tcl_SetResult(interp, result, freeProc)
21
22       const char *
23       Tcl_GetStringResult(interp)
24
25       Tcl_AppendResult(interp, result, result, ... , (char *) NULL)
26
27       Tcl_AppendResultVA(interp, argList)
28
29       Tcl_ResetResult(interp)
30
31       Tcl_TransferResult(sourceInterp, result, targetInterp)                  │
32
33       Tcl_AppendElement(interp, element)
34
35       Tcl_FreeResult(interp)
36

ARGUMENTS

38       Tcl_Interp *interp (out)                Interpreter  whose result is to
39                                               be modified or read.
40
41       Tcl_Obj *objPtr (in)                    Tcl value to become result  for
42                                               interp.
43
44       char *result (in)                       String  value  to become result
45                                               for interp or to be appended to
46                                               the existing result.
47
48       const char *element (in)                String  value  to  append  as a
49                                               list element  to  the  existing
50                                               result of interp.
51
52       Tcl_FreeProc *freeProc (in)             Address of procedure to call to
53                                               release storage at  result,  or
54                                               TCL_STATIC,   TCL_DYNAMIC,   or
55                                               TCL_VOLATILE.
56
57       va_list argList (in)                    An  argument  list  which  must
58                                               have   been  initialized  using
59                                               va_start,  and  cleared   using
60                                               va_end.
61
62       Tcl_Interp *sourceInterp (in)           Interpreter that the result and │
63                                               error  information  should   be │
64                                               copied from.
65
66       Tcl_Interp *targetInterp (in)           Interpreter that the result and │
67                                               error  information  should   be │
68                                               copied to.
69
70       int result (in)                         If   TCL_OK,   only   copy  the │
71                                               result. If TCL_ERROR, copy  the │
72                                               error information as well.
73______________________________________________________________________________
74

DESCRIPTION

76       The procedures described here are utilities for manipulating the result
77       value in a Tcl interpreter.  The interpreter result may be either a Tcl
78       value or a string.  For example, Tcl_SetObjResult and Tcl_SetResult set
79       the interpreter result to, respectively, a value and a  string.   Simi‐
80       larly,  Tcl_GetObjResult and Tcl_GetStringResult return the interpreter
81       result as a value and as a string.   The  procedures  always  keep  the
82       string and value forms of the interpreter result consistent.  For exam‐
83       ple, if Tcl_SetObjResult is called to set the result to a  value,  then
84       Tcl_GetStringResult is called, it will return the value's string repre‐
85       sentation.
86
87       Tcl_SetObjResult arranges for objPtr  to  be  the  result  for  interp,
88       replacing  any  existing  result.   The  result is left pointing to the
89       value referenced by objPtr.  objPtr's reference  count  is  incremented
90       since  there  is  now a new reference to it from interp.  The reference
91       count for any old result value is decremented and the old result  value
92       is freed if no references to it remain.
93
94       Tcl_GetObjResult returns the result for interp as a value.  The value's
95       reference count is not incremented; if the caller  needs  to  retain  a
96       long-term  pointer  to  the  value  they should use Tcl_IncrRefCount to
97       increment its reference count in order to keep it from being freed  too
98       early or accidentally changed.
99
100       Tcl_SetResult  arranges for result to be the result for the current Tcl
101       command in interp, replacing any existing result.  The  freeProc  argu‐
102       ment specifies how to manage the storage for the result argument; it is
103       discussed in the section THE  TCL_FREEPROC  ARGUMENT  TO  TCL_SETRESULT
104       below.   If  result is NULL, then freeProc is ignored and Tcl_SetResult
105       re-initializes interp's result to point to an empty string.
106
107       Tcl_GetStringResult returns the result for interp as a string.  If  the
108       result  was  set  to a value by a Tcl_SetObjResult call, the value form
109       will be converted to a string and returned.  If the value's string rep‐
110       resentation contains null bytes, this conversion will lose information.
111       For this reason, programmers are encouraged to write their code to  use
112       the new value API procedures and to call Tcl_GetObjResult instead.
113
114       Tcl_ResetResult  clears  the result for interp and leaves the result in
115       its normal empty initialized state.  If the result is a value, its ref‐
116       erence  count  is  decremented  and  the  result is left pointing to an
117       unshared value representing an empty string.  If the result is a dynam‐
118       ically allocated string, its memory is free*d and the result is left as
119       a empty string.  Tcl_ResetResult also clears the error state managed by
120       Tcl_AddErrorInfo, Tcl_AddObjErrorInfo, and Tcl_SetErrorCode.
121
122       Tcl_AppendResult  makes  it easy to build up Tcl results in pieces.  It
123       takes each of its result arguments and appends them  in  order  to  the
124       current  result  associated  with interp.  If the result is in its ini‐
125       tialized empty state (e.g. a command  procedure  was  just  invoked  or
126       Tcl_ResetResult was just called), then Tcl_AppendResult sets the result
127       to the concatenation of its result arguments.  Tcl_AppendResult may  be
128       called  repeatedly  as  additional  pieces  of the result are produced.
129       Tcl_AppendResult takes care of all the storage management issues  asso‐
130       ciated  with  managing  interp's  result,  such  as allocating a larger
131       result area if necessary.  It also manages conversion to and  from  the
132       result  field of the interp so as to handle backward-compatibility with
133       old-style extensions.  Any number of result arguments may be passed  in
134       a single call; the last argument in the list must be a NULL pointer.
135
136       Tcl_AppendResultVA  is the same as Tcl_AppendResult except that instead
137       of taking a variable number of arguments it takes an argument list.
138
139       Tcl_TransferResult moves a result  from  one  interpreter  to  another, │
140       optionally  (dependent  on  the  result  parameter) including the error │
141       information dictionary as well. The interpreters must be  in  the  same │
142       thread.   The  source  interpreter  will  have its result reset by this │
143       operation.
144

DEPRECATED INTERFACES

146   OLD STRING PROCEDURES
147       Use of the following procedures is deprecated since they manipulate the
148       Tcl  result  as  a  string.   Procedures  such as Tcl_SetObjResult that
149       manipulate the result as a value can be significantly more efficient.
150
151       Tcl_AppendElement is similar to  Tcl_AppendResult  in  that  it  allows
152       results  to  be  built  up in pieces.  However, Tcl_AppendElement takes
153       only a single element argument and it appends that argument to the cur‐
154       rent result as a proper Tcl list element.  Tcl_AppendElement adds back‐
155       slashes or braces if necessary to ensure that interp's  result  can  be
156       parsed  as  a  list and that element will be extracted as a single ele‐
157       ment.  Under normal conditions,  Tcl_AppendElement  will  add  a  space
158       character  to  interp's result just before adding the new list element,
159       so that the list elements in the result are properly  separated.   How‐
160       ever  if  the new list element is the first in a list or sub-list (i.e.
161       interp's current result is empty, or consists of the  single  character
162       “{”, or ends in the characters “ {”) then no space is added.
163
164       Tcl_FreeResult  performs part of the work of Tcl_ResetResult.  It frees
165       up  the  memory  associated  with  interp's  result.   It   also   sets
166       interp->freeProc  to  zero, but does not change interp->result or clear
167       error state.  Tcl_FreeResult is most commonly used when a procedure  is
168       about to replace one result value with another.
169
170   DIRECT ACCESS TO INTERP->RESULT
171       It   used  to  be  legal  for  programs  to  directly  read  and  write
172       interp->result to manipulate the interpreter result.  The  Tcl  headers
173       no  longer  permit  this access by default, and C code still doing this
174       must be updated to use supported  routines  Tcl_GetObjResult,  Tcl_Get‐
175       StringResult, Tcl_SetObjResult, and Tcl_SetResult.  As a migration aid,
176       access can be restored with the compiler directive
177              #define USE_INTERP_RESULT
178       but this is meant only to offer life support to otherwise dead code.
179

THE TCL_FREEPROC ARGUMENT TO TCL_SETRESULT

181       Tcl_SetResult's freeProc argument specifies how the Tcl  system  is  to
182       manage  the  storage  for  the  result  argument.   If Tcl_SetResult or
183       Tcl_SetObjResult are called at  a  time  when  interp  holds  a  string
184       result,  they  do  whatever  is  necessary to dispose of the old string
185       result (see the Tcl_Interp manual entry for details on this).
186
187       If freeProc is TCL_STATIC it means that result refers  to  an  area  of
188       static storage that is guaranteed not to be modified until at least the
189       next call to Tcl_Eval.  If freeProc is TCL_DYNAMIC it means that result
190       was  allocated  with a call to Tcl_Alloc and is now the property of the
191       Tcl system.  Tcl_SetResult will arrange for the string's storage to  be
192       released  by calling Tcl_Free when it is no longer needed.  If freeProc
193       is TCL_VOLATILE it means that result points to an area of  memory  that
194       is  likely to be overwritten when Tcl_SetResult returns (e.g. it points
195       to something in a stack frame).  In this case Tcl_SetResult will make a
196       copy of the string in dynamically allocated storage and arrange for the
197       copy to be the result for the current Tcl command.
198
199       If freeProc is not one  of  the  values  TCL_STATIC,  TCL_DYNAMIC,  and
200       TCL_VOLATILE,  then  it  is  the address of a procedure that Tcl should
201       call to free the string.  This allows applications to use  non-standard
202       storage  allocators.   When  Tcl  no  longer  needs the storage for the
203       string, it will call  freeProc.  FreeProc  should  have  arguments  and
204       result that match the type Tcl_FreeProc:
205
206              typedef void Tcl_FreeProc(
207                      char *blockPtr);
208
209       When  freeProc  is  called,  its  blockPtr  will be set to the value of
210       result passed to Tcl_SetResult.
211

SEE ALSO

213       Tcl_AddErrorInfo, Tcl_CreateObjCommand, Tcl_SetErrorCode, Tcl_Interp
214

KEYWORDS

216       append, command, element, list, value,  result,  return  value,  inter‐
217       preter
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220
221Tcl                                   8.0                     Tcl_SetResult(3)
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