Tcl_SetResult(3tcl) Tcl Library Procedures Tcl_SetResult(3tcl)
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NAME
Tcl_SetObjResult, Tcl_GetObjResult, Tcl_SetResult, Tcl_GetStringResult,
Tcl_AppendResult, Tcl_AppendResultVA, Tcl_AppendElement, Tcl_ResetRe-
sult, Tcl_TransferResult, Tcl_FreeResult - 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_AppendResultVA(interp, argList)
Tcl_ResetResult(interp)
Tcl_TransferResult(sourceInterp, code, targetInterp) │
Tcl_AppendElement(interp, element)
Tcl_FreeResult(interp)
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.
va_list argList (in) An argument list which must
have been initialized using
va_start, and cleared using
va_end.
Tcl_Interp *sourceInterp (in) Interpreter that the result and │
return options should be trans- │
ferred from.
Tcl_Interp *targetInterp (in) Interpreter that the result and │
return options should be trans- │
ferred to.
int code (in) Return code value that controls │
transfer of return options.
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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. Simi-
larly, 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 exam-
ple, if Tcl_SetObjResult is called to set the result to a value, then
Tcl_GetStringResult is called, it will return the value's string repre-
sentation.
Tcl_SetObjResult arranges for objPtr to be the result for interp, re-
placing 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 in-
crement 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 argu-
ment specifies how to manage the storage for the result argument; it is
discussed in the section THE TCL_FREEPROC ARGUMENT TO TCL_SETRESULT be-
low. 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 rep-
resentation 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 ref-
erence count is decremented and the result is left pointing to an un-
shared value representing an empty string. If the result is a dynami-
cally 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 ini-
tialized 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 asso-
ciated with managing interp's result, such as allocating a larger re-
sult area if necessary. It also manages conversion to and from the re-
sult 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 a NULL pointer.
Tcl_AppendResultVA is the same as Tcl_AppendResult except that instead
of taking a variable number of arguments it takes an argument list.
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 ma-
nipulate the result as a value can be significantly more efficient.
Tcl_AppendElement is similar to Tcl_AppendResult in that it allows re-
sults 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 back-
slashes 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 ele-
ment. 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. How-
ever 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.
Tcl_FreeResult performs part of the work of Tcl_ResetResult. It frees
up the memory associated with interp's result. It also sets in-
terp->freeProc to zero, but does not change interp->result or clear er-
ror state. Tcl_FreeResult is most commonly used when a procedure is
about to replace one result value with another.
DIRECT ACCESS TO INTERP->RESULT
It used to be legal for programs to directly read and write interp->re-
sult to manipulate the interpreter result. The Tcl headers no longer
permit this access by default, and C code still doing this must be up-
dated to use supported routines Tcl_GetObjResult, Tcl_GetStringResult,
Tcl_SetObjResult, and Tcl_SetResult. As a migration aid, access can be
restored with the compiler directive
#define USE_INTERP_RESULT
but this is meant only to offer life support to otherwise dead code.
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 re-
sult, 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 re-
sult that match the type Tcl_FreeProc:
typedef void Tcl_FreeProc(
char *blockPtr);
When freeProc is called, its blockPtr will be set to the value of re-
sult passed to Tcl_SetResult.
SEE ALSO
Tcl_AddErrorInfo, Tcl_CreateObjCommand, Tcl_SetErrorCode, Tcl_Interp,
Tcl_GetReturnOptions
KEYWORDS
append, command, element, list, value, result, return value, inter-
preter
Tcl 8.6 Tcl_SetResult(3tcl)
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