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Tcl_SetResult(3) Tcl Library Procedures Tcl_SetResult(3)
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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_SetObjResult(interp, objPtr)
Tcl_Obj *
Tcl_GetObjResult(interp)
Tcl_SetResult(interp, string, freeProc)
CONST 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 modi-
fied 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 ini-
tialised using
TCL_VARARGS_START, and
cleared using va_end.
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DESCRIPTION
The procedures described here are utilities for manipulat-
ing 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_GetStringRe-
sult 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 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
section THE TCL_FREEPROC ARGUMENT TO TCL_SETRESULT below.
If string is NULL, then freeProc is ignored and Tcl_SetRe-
sult 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_SetO-
bjResult 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 infor-
mation. 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 rep-
resenting 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_AddObjError-
Info, 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 command procedure was just invoked or
Tcl_ResetResult was just called), then Tcl_AppendResult
sets the result to the concatenation of its string argu-
ments. Tcl_AppendResult may be called repeatedly as addi-
tional pieces of the result are produced. Tcl_Appen-
dResult takes care of all the storage management issues
associated with managing interp's result, such as allocat-
ing 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 element. Under normal conditions, Tcl_AppendEle-
ment will add a space character to interp's result just
before adding the new list element, so that the list ele-
ments 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_ResetRe-
sult. 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
inconsistent. Programs should always read the result
using the procedures Tcl_GetObjResult or Tcl_GetStringRe-
sult, 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 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 applications to use non-standard storage alloca-
tors. When Tcl no longer needs the storage for the
string, it will call freeProc. FreeProc should have argu-
ments 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
Tcl 8.0 Tcl_SetResult(3)