Tcl_SetResult(3) Tcl Library Procedures Tcl_SetResult(3)
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NAME
Tcl_SetObjResult, Tcl_GetObjResult, Tcl_SetResult, Tcl_GetStringResult, Tcl_AppendResult, Tcl_Appen-dResultVA, Tcl_AppendResultVA,
dResultVA, 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, string, freeProc)
CONST char *
Tcl_GetStringResult(interp)
Tcl_AppendResult(interp, string, string, ... , (char *) NULL)
Tcl_AppendResultVA(interp, argList)
Tcl_AppendElement(interp, string)
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 *string (in) String value to become result for interp or to be appended to the
existing result.
Tcl_FreeProc *freeProc (in) Address of procedure to call to release storage at string, or
TCL_STATIC, TCL_DYNAMIC, or TCL_VOLATILE.
va_list argList (in) An argument list which must have been initialised using
TCL_VARARGS_START, and cleared using va_end.
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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
accidently changed.
Tcl_SetResult arranges for string 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 string argu-ment; argument;
ment; it is discussed in the section THE TCL_FREEPROC ARGUMENT TO TCL_SETRESULT below. If string 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 an 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 point-ing pointing
ing 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.
OLD STRING PROCEDURES
Use of the following procedures is deprecated since they manipulate the Tcl result as a string. Pro-cedures Procedures
cedures such as Tcl_SetObjResult that manipulate the result as an object can be significantly more
efficient.
Tcl_AppendResult makes it easy to build up Tcl results in pieces. It takes each of its string argu-ments arguments
ments 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. It also converts the current inter-preter interpreter
preter result from an object to a string, if necessary, before appending the argument strings. Any
number of string 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_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 neces-sary necessary
sary 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_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 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.
DIRECT ACCESS TO INTERP->RESULT IS DEPRECATED
It used to be legal for programs to directly read and write interp->result to manipulate the inter-preter interpreter
preter 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 pro-cedures procedures
cedures 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
string 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 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 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 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 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.
SEE ALSO
Tcl_AddErrorInfo, Tcl_CreateObjCommand, Tcl_SetErrorCode, Tcl_Interp
KEYWORDS
append, command, element, list, object, result, return value, interpreter
Tcl 8.0 Tcl_SetResult(3)
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