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NAME
Tcl_SetObjResult, Tcl_GetObjResult, Tcl_SetResult,
Tcl_GetStringResult, Tcl_AppendResult, Tcl_AppendResultVA,
Tcl_AppendElement, Tcl_ResetResult - manipulate Tcl result
SYNOPSIS
#include <tcl.h>
Tcl_SetObjResult(interp, objPtr)
Tcl_Obj *
Tcl_GetObjResult(interp)
Tcl_SetResult(interp, string, freeProc)
char *
Tcl_GetStringResult(interp)
Tcl_AppendResult(interp, string, string, ... , (char *) NULL)
Tcl_AppendResultVA(interp, argList)
Tcl_AppendElement(interp, string)
Tcl_ResetResult(interp)
Tcl_FreeResult(interp)
ARGUMENTS
Tcl_Interp *interp (out) Interpreter whose result
is to be modified or
read.
Tcl_Obj *objPtr (in) Object value to become
result for interp.
char *string (in) String value to become
result for interp or to
be appended to the
existing result.
Tcl_FreeProc *freeProc (in) Address of procedure to
call to release storage
at string, or
TCL_STATIC, TCL_DYNAMIC,
or TCL_VOLATILE.
va_list argList (in) An argument list which
must have been initial-
ised using
TCL_VARARGS_START, and
cleared using va_end.
_________________________________________________________________
DESCRIPTION
The procedures described here are utilities for manipulating
the result value in a Tcl interpreter. The interpreter
result may be either a Tcl object or a string. For example,
Tcl_SetObjResult and Tcl_SetResult set the interpreter
result to, respectively, an object and a string. Similarly,
Tcl_GetObjResult and Tcl_GetStringResult return the inter-
preter result as an object and as a string. The procedures
always keep the string and object forms of the interpreter
result consistent. For example, if Tcl_SetObjResult is
called to set the result to an object, then
Tcl_GetStringResult is called, it will return the object's
string value.
Tcl_SetObjResult arranges for objPtr to be the result for
interp, replacing any existing result. The result is left
pointing to the object 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 object is decremented and the old result object
is freed if no references to it remain.
Tcl_GetObjResult returns the result for interp as an object.
The object's reference count is not incremented; if the
caller needs to retain a long-term pointer to the object
they should use Tcl_IncrRefCount to increment its reference
count in order to keep it from being freed too early or
accidently changed.
Tcl_SetResult arranges for string 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 string argument; it is discussed in the sec-
tion THE TCL_FREEPROC ARGUMENT TO TCL_SETRESULT below. If
string 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 an
string. If the result was set to an object by a
Tcl_SetObjResult call, the object form will be converted to
a string and returned. If the object's string representa-
tion contains null bytes, this conversion will lose informa-
tion. For this reason, programmers are encouraged to write
their code to use the new object 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 an object, its reference count is decremented and the
result is left pointing to an unshared object 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.
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 an object can
be significantly more efficient.
Tcl_AppendResult makes it easy to build up Tcl results in
pieces. It takes each of its string 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 com-
mand procedure was just invoked or Tcl_ResetResult was just
called), then Tcl_AppendResult sets the result to the con-
catenation of its string 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 converts the current interpreter result from an object
to a string, if necessary, before appending the argument
strings. Any number of string 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_AppendElement is similar to Tcl_AppendResult in that it
allows results to be built up in pieces. However,
Tcl_AppendElement takes only a single string 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 string 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. 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 doesn't 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 IS DEPRECATED
It used to be legal for programs to directly read and write
interp->result to manipulate the interpreter result. Direct
access to interp->result is now strongly deprecated because
it can make the result's string and object forms incon-
sistent. Programs should always read the result using the
procedures Tcl_GetObjResult or Tcl_GetStringResult, and
write the result using Tcl_SetObjResult or Tcl_SetResult.
THE TCL_FREEPROC ARGUMENT TO TCL_SETRESULT
Tcl_SetResult's freeProc argument specifies how the Tcl sys-
tem is to manage the storage for the string 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 string 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 string 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 string 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 isn't 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 applica-
tions 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 string passed to Tcl_SetResult.
SEE ALSO
Tcl_AddErrorInfo, Tcl_CreateObjCommand, Tcl_SetErrorCode,
Tcl_Interp
KEYWORDS
append, command, element, list, object, result, return
value, interpreter
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