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

Provided by: tcl8.6-doc_8.6.10+dfsg-1_all

NAME

       Tcl_SetObjResult,  Tcl_GetObjResult, Tcl_SetResult, Tcl_GetStringResult, Tcl_AppendResult,
       Tcl_AppendResultVA, Tcl_AppendElement, Tcl_ResetResult, Tcl_TransferResult, 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_ResetResult(interp)

       Tcl_TransferResult(sourceInterp, result, targetInterp)                                     │

       Tcl_AppendElement(interp, element)

       Tcl_FreeResult(interp)

ARGUMENTS

Tcl_Interp *interp (out) Interpreter whose result is to be modified or
read.

Tcl_Obj *objPtr (in) Tcl value to become result for interp.

char *result (in) String value to become result for interp or to be
appended to the existing result.

const 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.

Tcl_Interp *sourceInterp (in) Interpreter that the result and error information │
should be copied from.

Tcl_Interp *targetInterp (in) Interpreter that the result and error information │
should be copied to.

int result (in) If TCL_OK, only copy the result. If TCL_ERROR, │
copy the error information as well.
_________________________________________________________________________________________________

DESCRIPTION

The procedures described here are utilities for manipulating the result value in a Tcl
interpreter. The interpreter result may be either a Tcl value or a string. For example,
Tcl_SetObjResult and Tcl_SetResult set the interpreter result to, respectively, a value
and a string. Similarly, Tcl_GetObjResult and Tcl_GetStringResult return the interpreter
result as a value and as a string. The procedures always keep the string and value forms
of the interpreter result consistent. For example, if Tcl_SetObjResult is called to set
the result to a value, then Tcl_GetStringResult is called, it will return the value's
string representation.

Tcl_SetObjResult arranges for objPtr to be the result for interp, replacing any existing
result. The result is left pointing to the value 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 value is decremented and the old result value is freed
if no references to it remain.

Tcl_GetObjResult returns the result for interp as a value. The value's reference count is
not incremented; if the caller needs to retain a long-term pointer to the value 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 a
value by a Tcl_SetObjResult call, the value form will be converted to a string and
returned. If the value'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 value 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 a value, its reference count is decremented and the
result is left pointing to an unshared value 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.

Tcl_TransferResult moves a result from one interpreter to another, optionally (dependent │
on the result parameter) including the error information dictionary as well. The │
interpreters must be in the same thread. The source interpreter will have its result │
reset by this operation.

DEPRECATED INTERFACES

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 a value 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
It used to be legal for programs to directly read and write interp->result to manipulate
the interpreter result. The Tcl headers no longer permit this access by default, and C
code still doing this must be updated to use supported routines Tcl_GetObjResult,
Tcl_GetStringResult, Tcl_SetObjResult, and Tcl_SetResult. As a migration aid, access can
be restored with the compiler directive
#define USE_INTERP_RESULT
but this is meant only to offer life support to otherwise dead code.

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, value, result, return value, interpreter