Manual Reference Pages - TCL_APPENDRESULTVA (3)
Tcl_SetObjResult, Tcl_GetObjResult, Tcl_SetResult, Tcl_GetStringResult, Tcl_AppendResult, Tcl_AppendResultVA, Tcl_AppendElement, Tcl_ResetResult, Tcl_FreeResult - manipulate Tcl result
Tcl_SetResult(interp, result, freeProc)
const char *
Tcl_AppendResult(interp, result, result, ... , (char *) NULL)
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
va_list argList (in)
An argument list which must have been initialized using
va_start, and cleared using va_end.
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 objects string value.
arranges for objPtr to be the result for interp,
replacing any existing result.
The result is left pointing to the object
referenced by objPtr.
objPtrs 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 objects 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.
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
re-initializes interps 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 objects 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_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 interps
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-compatability with old-style
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 interps 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 interps result just before adding the new
list element, so that the list elements in the result are properly
However if the new list element is the first in a list or sub-list
(i.e. interps current result is empty, or consists of the
or ends in the characters
then no space is added.
Tcl_FreeResult performs part of the work
It frees up the memory associated with interps 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 results 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_SetResults 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.
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 strings 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:
When freeProc is called, its blockPtr will be set to
the value of result passed to Tcl_SetResult.
typedef void Tcl_FreeProc(char *blockPtr);
Tcl_AddErrorInfo, Tcl_CreateObjCommand, Tcl_SetErrorCode, Tcl_Interp
append, command, element, list, object, result, return value, interpreter
|Tcl ||TCL_SETRESULT (3) ||8.0 |
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