NAME¶
Tcl_SetObjResult, Tcl_GetObjResult, Tcl_SetResult, Tcl_GetStringResult,
Tcl_AppendResult, Tcl_AppendResultVA, Tcl_AppendElement, Tcl_ResetResult,
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_AppendElement(interp, element)
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 *result (in)
- String value to become result for interp or to be
appended to the existing result.
- 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.
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 interpreter
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 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 an object by a
Tcl_SetObjResult call, the object
form will be converted to a string and returned. If the object'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
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.
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 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.
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_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 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 inconsistent. 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 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.
SEE ALSO¶
Tcl_AddErrorInfo, Tcl_CreateObjCommand, Tcl_SetErrorCode, Tcl_Interp
KEYWORDS¶
append, command, element, list, object, result, return value, interpreter