SetResult
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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 modified.
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.
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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
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 malloc() and is now the
property of the Tcl system. Tcl_SetResult will arrange for
the string's storage to be released by calling 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 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 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 string passed to Tcl_SetResult.
If string is NULL, then freeProc is ignored and
Tcl_SetResult 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 dispose
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_ResetResult 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_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_ResetResult clears the result for interp, freeing the
memory associated with it if the current result was
dynamically allocated. It leaves the result in its normal
initialized 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_SetErrorCode.
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