Tcl_SetResult(3) Tcl Library Procedures Tcl_SetResult(3)_________________________________________________________________NAME
Tcl_SetResult, Tcl_AppendResult, Tcl_AppendElement,
Tcl_ResetResult - manipulate Tcl result string
SYNOPSIS
#include <tcl.h>
Tcl_SetResult(interp, string, freeProc)
Tcl_AppendResult(interp, string, string, ... , (char *) NULL)
Tcl_AppendElement(interp, string)
Tcl_ResetResult(interp)Tcl_FreeResult(interp)ARGUMENTS
Tcl_Interp *interp (out) Interpreter whose
result is to be modi-
fied.
char *string (in) String value to become
result for interp or
to be appended to
existing result.
Tcl_FreeProc *freeProc (in) Address of procedure
to call to release
storage at string, or
TCL_STATIC,
TCL_DYNAMIC, or
TCL_VOLATILE.
_________________________________________________________________DESCRIPTION
The procedures described here are utilities for setting
the result/error string in a Tcl interpreter.
Tcl_SetResult arranges for string to be the return string
for the current Tcl command in interp, replacing any
existing result. If freeProc is TCL_STATIC it means that
string refers to an area of static storage that is guaran-
teed 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
Tcl 7.5 1
Tcl_SetResult(3) Tcl Library Procedures Tcl_SetResult(3)
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 return string 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.
If string is NULL, then freeProc is ignored and Tcl_SetRe-
sult re-initializes interp's result to point to the pre-
allocated result area, with an empty string in the result
area.
If Tcl_SetResult is called at a time when interp holds a
result, Tcl_SetResult does whatever is necessary to dis-
pose of the old result (see the Tcl_Interp manual entry
for details on this).
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_ResetRe-
sult was just called), then Tcl_AppendResult sets the
result to the concatenation of its string 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. Any number of string arguments
may be passed in a single call; the last argument in the
list must be a NULL pointer.
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
Tcl 7.5 2
Tcl_SetResult(3) Tcl Library Procedures Tcl_SetResult(3)
single character ``{'', or ends in the characters `` {'')
then no space is added.
Tcl_ResetResult clears the result for interp, freeing the
memory associated with it if the current result was dynam-
ically allocated. It leaves the result in its normal ini-
tialized state with interp->result pointing to a static
buffer containing TCL_RESULT_SIZE characters, of which the
first character is zero. Tcl_ResetResult also clears the
error state managed by Tcl_AddErrorInfo and Tcl_SetError-
Code.
Tcl_FreeResult is a macro that performs part of the work
of Tcl_ResetResult. It frees up the memory associated
with interp's result and sets interp->freeProc to zero,
but it 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.
SEE ALSO
Tcl_AddErrorInfo, Tcl_SetErrorCode, Tcl_Interp
KEYWORDS
append, command, element, list, result, return value,
interpreter
Tcl 7.5 3
