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, string, freeProc)
21 CONST char *
23 Tcl_GetStringResult(interp)
24 Tcl_AppendResult(interp, string, string, ... , (char *) NULL)
26 Tcl_AppendResultVA(interp, argList)
28 Tcl_AppendElement(interp, string)
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 *string (in) String value to become result for
43 interp or to be appended to the
44 existing result.
45 Tcl_FreeProc *freeProc (in) Address of procedure to call to
47 release storage at string, or
48 TCL_STATIC, TCL_DYNAMIC, or
49 TCL_VOLATILE.
50 va_list argList (in) An argument list which must have
52 been initialised using
53 TCL_VARARGS_START, and cleared
54 using va_end.
55_________________________________________________________________
56
59 The procedures described here are utilities for manipulating the result
60 value in a Tcl interpreter. The interpreter result may be either a Tcl
61 object or a string. For example, Tcl_SetObjResult and Tcl_SetResult
62 set the interpreter result to, respectively, an object and a string.
63 Similarly, Tcl_GetObjResult and Tcl_GetStringResult return the inter‐
64 preter result as an object and as a string. The procedures always keep
65 the string and object forms of the interpreter result consistent. For
66 example, if Tcl_SetObjResult is called to set the result to an object,
67 then Tcl_GetStringResult is called, it will return the object's string
68 value.
69 Tcl_SetObjResult arranges for objPtr to be the result for interp,
71 replacing any existing result. The result is left pointing to the
72 object referenced by objPtr. objPtr's reference count is incremented
73 since there is now a new reference to it from interp. The reference
74 count for any old result object is decremented and the old result
75 object is freed if no references to it remain.
76 Tcl_GetObjResult returns the result for interp as an object. The
78 object's reference count is not incremented; if the caller needs to
79 retain a long-term pointer to the object they should use Tcl_IncrRef‐
80 Count to increment its reference count in order to keep it from being
81 freed too early or accidently changed.
82 Tcl_SetResult arranges for string to be the result for the current Tcl
84 command in interp, replacing any existing result. The freeProc argu‐
85 ment specifies how to manage the storage for the string argument; it is
86 discussed in the section THE TCL_FREEPROC ARGUMENT TO TCL_SETRESULT
87 below. If string is NULL, then freeProc is ignored and Tcl_SetResult
88 re-initializes interp's result to point to an empty string.
89 Tcl_GetStringResult returns the result for interp as an string. If the
91 result was set to an object by a Tcl_SetObjResult call, the object form
92 will be converted to a string and returned. If the object's string
93 representation contains null bytes, this conversion will lose informa‐
94 tion. For this reason, programmers are encouraged to write their code
95 to use the new object API procedures and to call Tcl_GetObjResult
96 instead.
97 Tcl_ResetResult clears the result for interp and leaves the result in
99 its normal empty initialized state. If the result is an object, its
100 reference count is decremented and the result is left pointing to an
101 unshared object representing an empty string. If the result is a
102 dynamically allocated string, its memory is free*d and the result is
103 left as a empty string. Tcl_ResetResult also clears the error state
104 managed by Tcl_AddErrorInfo, Tcl_AddObjErrorInfo, and Tcl_SetErrorCode.
105
108 Use of the following procedures is deprecated since they manipulate the
109 Tcl result as a string. Procedures such as Tcl_SetObjResult that
110 manipulate the result as an object can be significantly more efficient.
111 Tcl_AppendResult makes it easy to build up Tcl results in pieces. It
113 takes each of its string arguments and appends them in order to the
114 current result associated with interp. If the result is in its ini‐
115 tialized empty state (e.g. a command procedure was just invoked or
116 Tcl_ResetResult was just called), then Tcl_AppendResult sets the result
117 to the concatenation of its string arguments. Tcl_AppendResult may be
118 called repeatedly as additional pieces of the result are produced.
119 Tcl_AppendResult takes care of all the storage management issues asso‐
120 ciated with managing interp's result, such as allocating a larger
121 result area if necessary. It also converts the current interpreter
122 result from an object to a string, if necessary, before appending the
123 argument strings. Any number of string arguments may be passed in a
124 single call; the last argument in the list must be a NULL pointer.
125 Tcl_AppendResultVA is the same as Tcl_AppendResult except that instead
127 of taking a variable number of arguments it takes an argument list.
128 Tcl_AppendElement is similar to Tcl_AppendResult in that it allows
130 results to be built up in pieces. However, Tcl_AppendElement takes
131 only a single string argument and it appends that argument to the cur‐
132 rent result as a proper Tcl list element. Tcl_AppendElement adds back‐
133 slashes or braces if necessary to ensure that interp's result can be
134 parsed as a list and that string will be extracted as a single element.
135 Under normal conditions, Tcl_AppendElement will add a space character
136 to interp's result just before adding the new list element, so that the
137 list elements in the result are properly separated. However if the new
138 list element is the first in a list or sub-list (i.e. interp's current
139 result is empty, or consists of the single character ``{'', or ends in
140 the characters `` {'') then no space is added.
141 Tcl_FreeResult performs part of the work of Tcl_ResetResult. It frees
143 up the memory associated with interp's result. It also sets
144 interp->freeProc to zero, but doesn't change interp->result or clear
145 error state. Tcl_FreeResult is most commonly used when a procedure is
146 about to replace one result value with another.
147
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
160 Tcl_SetResult's freeProc argument specifies how the Tcl system is to
161 manage the storage for the string argument. If Tcl_SetResult or
162 Tcl_SetObjResult are called at a time when interp holds a string
163 result, they do whatever is necessary to dispose of the old string
164 result (see the Tcl_Interp manual entry for details on this).
165 If freeProc is TCL_STATIC it means that string refers to an area of
167 static storage that is guaranteed not to be modified until at least the
168 next call to Tcl_Eval. If freeProc is TCL_DYNAMIC it means that string
169 was allocated with a call to Tcl_Alloc and is now the property of the
170 Tcl system. Tcl_SetResult will arrange for the string's storage to be
171 released by calling Tcl_Free when it is no longer needed. If freeProc
172 is TCL_VOLATILE it means that string points to an area of memory that
173 is likely to be overwritten when Tcl_SetResult returns (e.g. it points
174 to something in a stack frame). In this case Tcl_SetResult will make a
175 copy of the string in dynamically allocated storage and arrange for the
176 copy to be the result for the current Tcl command.
177 If freeProc isn't one of the values TCL_STATIC, TCL_DYNAMIC, and
179 TCL_VOLATILE, then it is the address of a procedure that Tcl should
180 call to free the string. This allows applications to use non-standard
181 storage allocators. When Tcl no longer needs the storage for the
182 string, it will call freeProc. FreeProc should have arguments and
183 result that match the type Tcl_FreeProc:
184 typedef void Tcl_FreeProc(char *blockPtr);
185 When freeProc is called, its blockPtr will be set to the value of
186 string passed to Tcl_SetResult.
187
190 Tcl_AddErrorInfo, Tcl_CreateObjCommand, Tcl_SetErrorCode, Tcl_Interp
191
194 append, command, element, list, object, result, return value, inter‐
195 preter
196Tcl 8.0 Tcl_SetResult(3)