1Tcl_SetResult(3) Tcl Library Procedures Tcl_SetResult(3)
2______________________________________________________________________________
6
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
13 #include <tcl.h>
14 Tcl_SetObjResult(interp, objPtr)
16 Tcl_Obj *
18 Tcl_GetObjResult(interp)
19 Tcl_SetResult(interp, result, freeProc)
21 const char *
23 Tcl_GetStringResult(interp)
24 Tcl_AppendResult(interp, result, result, ... , (char *) NULL)
26 Tcl_AppendResultVA(interp, argList)
28 Tcl_ResetResult(interp)
30 Tcl_TransferResult(sourceInterp, code, targetInterp) │
32 Tcl_AppendElement(interp, element)
34 Tcl_FreeResult(interp)
36
38 Tcl_Interp *interp (out) Interpreter whose result is to
39 be modified or read.
40 Tcl_Obj *objPtr (in) Tcl value to become result for
42 interp.
43 char *result (in) String value to become result
45 for interp or to be appended to
46 the existing result.
47 const char *element (in) String value to append as a
49 list element to the existing
50 result of interp.
51 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 va_list argList (in) An argument list which must
58 have been initialized using
59 va_start, and cleared using
60 va_end.
61 Tcl_Interp *sourceInterp (in) Interpreter that the result and │
63 return options should be trans‐ │
64 ferred from.
65 Tcl_Interp *targetInterp (in) Interpreter that the result and │
67 return options should be trans‐ │
68 ferred to.
69 int code (in) Return code value that controls │
71 transfer of return options.
72______________________________________________________________________________
73
75 The procedures described here are utilities for manipulating the result
76 value in a Tcl interpreter. The interpreter result may be either a Tcl
77 value or a string. For example, Tcl_SetObjResult and Tcl_SetResult set
78 the interpreter result to, respectively, a value and a string. Simi‐
79 larly, Tcl_GetObjResult and Tcl_GetStringResult return the interpreter
80 result as a value and as a string. The procedures always keep the
81 string and value forms of the interpreter result consistent. For exam‐
82 ple, if Tcl_SetObjResult is called to set the result to a value, then
83 Tcl_GetStringResult is called, it will return the value's string repre‐
84 sentation.
85 Tcl_SetObjResult arranges for objPtr to be the result for interp, re‐
87 placing any existing result. The result is left pointing to the value
88 referenced by objPtr. objPtr's reference count is incremented since
89 there is now a new reference to it from interp. The reference count
90 for any old result value is decremented and the old result value is
91 freed if no references to it remain.
92 Tcl_GetObjResult returns the result for interp as a value. The value's
94 reference count is not incremented; if the caller needs to retain a
95 long-term pointer to the value they should use Tcl_IncrRefCount to in‐
96 crement its reference count in order to keep it from being freed too
97 early or accidentally changed.
98 Tcl_SetResult arranges for result to be the result for the current Tcl
100 command in interp, replacing any existing result. The freeProc argu‐
101 ment specifies how to manage the storage for the result argument; it is
102 discussed in the section THE TCL_FREEPROC ARGUMENT TO TCL_SETRESULT be‐
103 low. If result is NULL, then freeProc is ignored and Tcl_SetResult re-
104 initializes interp's result to point to an empty string.
105 Tcl_GetStringResult returns the result for interp as a string. If the
107 result was set to a value by a Tcl_SetObjResult call, the value form
108 will be converted to a string and returned. If the value's string rep‐
109 resentation contains null bytes, this conversion will lose information.
110 For this reason, programmers are encouraged to write their code to use
111 the new value API procedures and to call Tcl_GetObjResult instead.
112 Tcl_ResetResult clears the result for interp and leaves the result in
114 its normal empty initialized state. If the result is a value, its ref‐
115 erence count is decremented and the result is left pointing to an un‐
116 shared value representing an empty string. If the result is a dynami‐
117 cally allocated string, its memory is free*d and the result is left as
118 a empty string. Tcl_ResetResult also clears the error state managed by
119 Tcl_AddErrorInfo, Tcl_AddObjErrorInfo, and Tcl_SetErrorCode.
120 Tcl_AppendResult makes it easy to build up Tcl results in pieces. It
122 takes each of its result arguments and appends them in order to the
123 current result associated with interp. If the result is in its ini‐
124 tialized empty state (e.g. a command procedure was just invoked or
125 Tcl_ResetResult was just called), then Tcl_AppendResult sets the result
126 to the concatenation of its result arguments. Tcl_AppendResult may be
127 called repeatedly as additional pieces of the result are produced.
128 Tcl_AppendResult takes care of all the storage management issues asso‐
129 ciated with managing interp's result, such as allocating a larger re‐
130 sult area if necessary. It also manages conversion to and from the re‐
131 sult field of the interp so as to handle backward-compatibility with
132 old-style extensions. Any number of result arguments may be passed in
133 a single call; the last argument in the list must be a NULL pointer.
134 Tcl_AppendResultVA is the same as Tcl_AppendResult except that instead
136 of taking a variable number of arguments it takes an argument list.
137 Tcl_TransferResult transfers interpreter state from sourceInterp to │
139 targetInterp. The two interpreters must have been created in the same │
140 thread. If sourceInterp and targetInterp are the same, nothing is │
141 done. Otherwise, Tcl_TransferResult moves the result from sourceInterp │
142 to targetInterp, and resets the result in sourceInterp. It also moves │
143 the return options dictionary as controlled by the return code value │
144 code in the same manner as Tcl_GetReturnOptions.
145
147 OLD STRING PROCEDURES
148 Use of the following procedures is deprecated since they manipulate the
149 Tcl result as a string. Procedures such as Tcl_SetObjResult that ma‐
150 nipulate the result as a value can be significantly more efficient.
151 Tcl_AppendElement is similar to Tcl_AppendResult in that it allows re‐
153 sults to be built up in pieces. However, Tcl_AppendElement takes only
154 a single element argument and it appends that argument to the current
155 result as a proper Tcl list element. Tcl_AppendElement adds back‐
156 slashes or braces if necessary to ensure that interp's result can be
157 parsed as a list and that element will be extracted as a single ele‐
158 ment. Under normal conditions, Tcl_AppendElement will add a space
159 character to interp's result just before adding the new list element,
160 so that the list elements in the result are properly separated. How‐
161 ever if the new list element is the first in a list or sub-list (i.e.
162 interp's current result is empty, or consists of the single character
163 “{”, or ends in the characters “ {”) then no space is added.
164 Tcl_FreeResult performs part of the work of Tcl_ResetResult. It frees
166 up the memory associated with interp's result. It also sets in‐
167 terp->freeProc to zero, but does not change interp->result or clear er‐
168 ror state. Tcl_FreeResult is most commonly used when a procedure is
169 about to replace one result value with another.
170 DIRECT ACCESS TO INTERP->RESULT
172 It used to be legal for programs to directly read and write interp->re‐
173 sult to manipulate the interpreter result. The Tcl headers no longer
174 permit this access by default, and C code still doing this must be up‐
175 dated to use supported routines Tcl_GetObjResult, Tcl_GetStringResult,
176 Tcl_SetObjResult, and Tcl_SetResult. As a migration aid, access can be
177 restored with the compiler directive
178 #define USE_INTERP_RESULT
179 but this is meant only to offer life support to otherwise dead code.
180
182 Tcl_SetResult's freeProc argument specifies how the Tcl system is to
183 manage the storage for the result argument. If Tcl_SetResult or
184 Tcl_SetObjResult are called at a time when interp holds a string re‐
185 sult, they do whatever is necessary to dispose of the old string result
186 (see the Tcl_Interp manual entry for details on this).
187 If freeProc is TCL_STATIC it means that result refers to an area of
189 static storage that is guaranteed not to be modified until at least the
190 next call to Tcl_Eval. If freeProc is TCL_DYNAMIC it means that result
191 was allocated with a call to Tcl_Alloc and is now the property of the
192 Tcl system. Tcl_SetResult will arrange for the string's storage to be
193 released by calling Tcl_Free when it is no longer needed. If freeProc
194 is TCL_VOLATILE it means that result points to an area of memory that
195 is likely to be overwritten when Tcl_SetResult returns (e.g. it points
196 to something in a stack frame). In this case Tcl_SetResult will make a
197 copy of the string in dynamically allocated storage and arrange for the
198 copy to be the result for the current Tcl command.
199 If freeProc is not one of the values TCL_STATIC, TCL_DYNAMIC, and
201 TCL_VOLATILE, then it is the address of a procedure that Tcl should
202 call to free the string. This allows applications to use non-standard
203 storage allocators. When Tcl no longer needs the storage for the
204 string, it will call freeProc. FreeProc should have arguments and re‐
205 sult that match the type Tcl_FreeProc:
206 typedef void Tcl_FreeProc(
208 char *blockPtr);
209 When freeProc is called, its blockPtr will be set to the value of re‐
211 sult passed to Tcl_SetResult.
212
214 Tcl_AddErrorInfo, Tcl_CreateObjCommand, Tcl_SetErrorCode, Tcl_Interp,
215 Tcl_GetReturnOptions
216
218 append, command, element, list, value, result, return value, inter‐
219 preter
220Tcl 8.6 Tcl_SetResult(3)