Tribblix: manual page: Tcl

Tcl_SetResult(3) Tcl Library Procedures Tcl_SetResult(3)

____________________________________________________________________________

NAME

Tcl_SetObjResult, Tcl_GetObjResult, Tcl_SetResult,
Tcl_GetStringResult, Tcl_AppendResult, Tcl_AppendResultVA,
Tcl_AppendElement, Tcl_ResetResult, 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 |
transferred from.

Tcl_Interp *targetInterp (in) Interpreter that the result |
and return options should be |
transferred to.

int code (in) Return code value that |
controls transfer of return |
options.
____________________________________________________________________________

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. Similarly, 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 example, if Tcl_SetObjResult is called to set
the result to a value, then Tcl_GetStringResult is called, it will
return the value's string representation.

Tcl_SetObjResult arranges for objPtr to be the result for interp,
replacing 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 increment 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
argument specifies how to manage the storage for the result argument;
it is discussed in the section THE TCL_FREEPROC ARGUMENT TO
TCL_SETRESULT below. 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 representation 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
reference count is decremented and the result is left pointing to an
unshared value representing an empty string. If the result is a
dynamically 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
initialized 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 associated with managing interp's result, such as
allocating a larger result area if necessary. It also manages
conversion to and from the result 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 (char *)NULL.

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
manipulate the result as a value can be significantly more efficient.

Tcl_AppendElement is similar to Tcl_AppendResult in that it allows
results 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
backslashes 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
element. 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.
However 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
interp->freeProc to zero, but does not change interp->result or clear
error 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->result to manipulate the interpreter result. The Tcl headers
no longer permit this access by default, and C code still doing this
must be updated 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
result, 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 result 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
result passed to Tcl_SetResult.

KEYWORDS

append, command, element, list, value, result, return value,
interpreter

Tcl 8.6 Tcl_SetResult(3)