Ubuntu Manpage: Tcl_SetObjResult, Tcl_GetObjResult, Tcl_SetResult, Tcl_GetStringResult, Tcl

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.

KEYWORDS

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