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_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_AppendElement(interp, element)
30 Tcl_ResetResult(interp)
32 Tcl_FreeResult(interp)
34
36 Tcl_Interp *interp (out) Interpreter whose result is to be
37 modified or read.
38 Tcl_Obj *objPtr (in) Object value to become result for
40 interp.
41 char *result (in) String value to become result for
43 interp or to be appended to the
44 existing result.
45 char *element (in) String value to append as a list
47 element to the existing result of
48 interp.
49 Tcl_FreeProc *freeProc (in) Address of procedure to call to
51 release storage at result, or
52 TCL_STATIC, TCL_DYNAMIC, or
53 TCL_VOLATILE.
54 va_list argList (in) An argument list which must have
56 been initialized using va_start,
57 and cleared using va_end.
58_________________________________________________________________
59
61 The procedures described here are utilities for manipulating the result
62 value in a Tcl interpreter. The interpreter result may be either a Tcl
63 object or a string. For example, Tcl_SetObjResult and Tcl_SetResult
64 set the interpreter result to, respectively, an object and a string.
65 Similarly, Tcl_GetObjResult and Tcl_GetStringResult return the inter‐
66 preter result as an object and as a string. The procedures always keep
67 the string and object forms of the interpreter result consistent. For
68 example, if Tcl_SetObjResult is called to set the result to an object,
69 then Tcl_GetStringResult is called, it will return the object's string
70 value.
71 Tcl_SetObjResult arranges for objPtr to be the result for interp,
73 replacing any existing result. The result is left pointing to the
74 object referenced by objPtr. objPtr's reference count is incremented
75 since there is now a new reference to it from interp. The reference
76 count for any old result object is decremented and the old result
77 object is freed if no references to it remain.
78 Tcl_GetObjResult returns the result for interp as an object. The
80 object's reference count is not incremented; if the caller needs to
81 retain a long-term pointer to the object they should use Tcl_IncrRef‐
82 Count to increment its reference count in order to keep it from being
83 freed too early or accidentally changed.
84 Tcl_SetResult arranges for result to be the result for the current Tcl
86 command in interp, replacing any existing result. The freeProc argu‐
87 ment specifies how to manage the storage for the result argument; it is
88 discussed in the section THE TCL_FREEPROC ARGUMENT TO TCL_SETRESULT
89 below. If result is NULL, then freeProc is ignored and Tcl_SetResult
90 re-initializes interp's result to point to an empty string.
91 Tcl_GetStringResult returns the result for interp as a string. If the
93 result was set to an object by a Tcl_SetObjResult call, the object form
94 will be converted to a string and returned. If the object's string
95 representation contains null bytes, this conversion will lose informa‐
96 tion. For this reason, programmers are encouraged to write their code
97 to use the new object API procedures and to call Tcl_GetObjResult
98 instead.
99 Tcl_ResetResult clears the result for interp and leaves the result in
101 its normal empty initialized state. If the result is an object, its
102 reference count is decremented and the result is left pointing to an
103 unshared object representing an empty string. If the result is a
104 dynamically allocated string, its memory is free*d and the result is
105 left as a empty string. Tcl_ResetResult also clears the error state
106 managed by Tcl_AddErrorInfo, Tcl_AddObjErrorInfo, and Tcl_SetErrorCode.
107 Tcl_AppendResult makes it easy to build up Tcl results in pieces. It
109 takes each of its result arguments and appends them in order to the
110 current result associated with interp. If the result is in its ini‐
111 tialized empty state (e.g. a command procedure was just invoked or
112 Tcl_ResetResult was just called), then Tcl_AppendResult sets the result
113 to the concatenation of its result arguments. Tcl_AppendResult may be
114 called repeatedly as additional pieces of the result are produced.
115 Tcl_AppendResult takes care of all the storage management issues asso‐
116 ciated with managing interp's result, such as allocating a larger
117 result area if necessary. It also manages conversion to and from the
118 result field of the interp so as to handle backward-compatibility with
119 old-style extensions. Any number of result arguments may be passed in
120 a single call; the last argument in the list must be a NULL pointer.
121 Tcl_AppendResultVA is the same as Tcl_AppendResult except that instead
123 of taking a variable number of arguments it takes an argument list.
124
126 Use of the following procedures (is deprecated since they manipulate
127 the Tcl result as a string. Procedures such as Tcl_SetObjResult that
128 manipulate the result as an object can be significantly more efficient.
129 Tcl_AppendElement is similar to Tcl_AppendResult in that it allows
131 results to be built up in pieces. However, Tcl_AppendElement takes
132 only a single element argument and it appends that argument to the cur‐
133 rent result as a proper Tcl list element. Tcl_AppendElement adds back‐
134 slashes or braces if necessary to ensure that interp's result can be
135 parsed as a list and that element will be extracted as a single ele‐
136 ment. Under normal conditions, Tcl_AppendElement will add a space
137 character to interp's result just before adding the new list element,
138 so that the list elements in the result are properly separated. How‐
139 ever if the new list element is the first in a list or sub-list (i.e.
140 interp's current result is empty, or consists of the single character
141 “{”, or ends in the characters “ {”) then no space is added.
142 Tcl_FreeResult performs part of the work of Tcl_ResetResult. It frees
144 up the memory associated with interp's result. It also sets
145 interp->freeProc to zero, but does not change interp->result or clear
146 error state. Tcl_FreeResult is most commonly used when a procedure is
147 about to replace one result value with another.
148
150 It used to be legal for programs to directly read and write
151 interp->result to manipulate the interpreter result. Direct access to
152 interp->result is now strongly deprecated because it can make the
153 result's string and object forms inconsistent. Programs should always
154 read the result using the procedures Tcl_GetObjResult or Tcl_Get‐
155 StringResult, and write the result using Tcl_SetObjResult or Tcl_SetRe‐
156 sult.
157
159 Tcl_SetResult's freeProc argument specifies how the Tcl system is to
160 manage the storage for the result argument. If Tcl_SetResult or
161 Tcl_SetObjResult are called at a time when interp holds a string
162 result, they do whatever is necessary to dispose of the old string
163 result (see the Tcl_Interp manual entry for details on this).
164 If freeProc is TCL_STATIC it means that result refers to an area of
166 static storage that is guaranteed not to be modified until at least the
167 next call to Tcl_Eval. If freeProc is TCL_DYNAMIC it means that result
168 was allocated with a call to Tcl_Alloc and is now the property of the
169 Tcl system. Tcl_SetResult will arrange for the string's storage to be
170 released by calling Tcl_Free when it is no longer needed. If freeProc
171 is TCL_VOLATILE it means that result points to an area of memory that
172 is likely to be overwritten when Tcl_SetResult returns (e.g. it points
173 to something in a stack frame). In this case Tcl_SetResult will make a
174 copy of the string in dynamically allocated storage and arrange for the
175 copy to be the result for the current Tcl command.
176 If freeProc is not one of the values TCL_STATIC, TCL_DYNAMIC, and
178 TCL_VOLATILE, then it is the address of a procedure that Tcl should
179 call to free the string. This allows applications to use non-standard
180 storage allocators. When Tcl no longer needs the storage for the
181 string, it will call freeProc. FreeProc should have arguments and
182 result that match the type Tcl_FreeProc:
183 typedef void Tcl_FreeProc(char *blockPtr);
184 When freeProc is called, its blockPtr will be set to the value of
185 result passed to Tcl_SetResult.
186
188 Tcl_AddErrorInfo, Tcl_CreateObjCommand, Tcl_SetErrorCode, Tcl_Interp
189
191 append, command, element, list, object, result, return value, inter‐
192 preter
193Tcl 8.0 Tcl_SetResult(3)