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.so man.macros

.TH Tcl_SetResult 3 7.5 Tcl "Tcl Library Procedures"

.BS

.SH NAME

Tcl_SetObjResult, Tcl_GetObjResult, Tcl_SetResult, Tcl_GetStringResult, Tcl_AppendResult, Tcl_AppendElement, Tcl_ResetResult \- manipulate Tcl result

.SH SYNOPSIS

.nf

\fB#include \fR

.sp

\fBTcl_SetObjResult\fR(\fIinterp, objPtr\fR)

.sp

Tcl_Obj *

\fBTcl_GetObjResult\fR(\fIinterp\fR)

.sp

\fBTcl_SetResult\fR(\fIinterp, string, freeProc\fR)

.sp

char *

\fBTcl_GetStringResult\fR(\fIinterp\fR)

.sp

\fBTcl_AppendResult\fR(\fIinterp, string, string, ... , \fB(char *) NULL\fR)

.sp

\fBTcl_AppendElement\fR(\fIinterp, string\fR)

.sp

\fBTcl_ResetResult\fR(\fIinterp\fR)

.sp

\fBTcl_FreeResult\fR(\fIinterp\fR)

.SH ARGUMENTS

.AS Tcl_FreeProc freeProc

.AP Tcl_Interp *interp out

Interpreter whose result is to be modified or read.

.AP Tcl_Obj *objPtr in

Object value to become result for \fIinterp\fR.

.AP char *string in

String value to become result for \fIinterp\fR or to be

appended to the existing result.

.AP Tcl_FreeProc *freeProc in

Address of procedure to call to release storage at

\fIstring\fR, or \fBTCL_STATIC\fR, \fBTCL_DYNAMIC\fR, or

\fBTCL_VOLATILE\fR.

.BE

.SH DESCRIPTION

.PP

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, \fBTcl_SetObjResult\fR and \fBTcl_SetResult\fR

set the interpreter result to, respectively, an object and a string.

Similarly, \fBTcl_GetObjResult\fR and \fBTcl_GetStringResult\fR

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 \fBTcl_SetObjResult\fR is called to set

the result to an object,

then \fBTcl_GetStringResult\fR is called,

it will return the object's string value.

.PP

\fBTcl_SetObjResult\fR

arranges for \fIobjPtr\fR to be the result for \fIinterp\fR,

replacing any existing result.

The result is left pointing to the object

referenced by \fIobjPtr\fR.

\fIobjPtr\fR's reference count is incremented

since there is now a new reference to it from \fIinterp\fR.

The reference count for any old result object

is decremented and the old result object is freed if no

references to it remain.

.PP

\fBTcl_GetObjResult\fR returns the result for \fIinterp\fR 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 \fBTcl_IncrRefCount\fR to increment its reference count

in order to keep it from being freed too early or accidently changed.

.PP

\fBTcl_SetResult\fR

arranges for \fIstring\fR to be the result for the current Tcl

command in \fIinterp\fR, replacing any existing result.

The \fIfreeProc\fR argument specifies how to manage the storage

for the \fIstring\fR argument;

it is discussed in the section

\fBTHE TCL_FREEPROC ARGUMENT TO TCL_SETRESULT\fR below.

If \fIstring\fR is \fBNULL\fR, then \fIfreeProc\fR is ignored

and \fBTcl_SetResult\fR

re-initializes \fIinterp\fR's result to point to an empty string.

.PP

\fBTcl_GetStringResult\fR returns the result for \fIinterp\fR as an string.

If the result was set to an object by a \fBTcl_SetObjResult\fR 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 \fBTcl_GetObjResult\fR instead.

.PP

\fBTcl_ResetResult\fR clears the result for \fIinterp\fR

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.

\fBTcl_ResetResult\fR also clears the error state managed by

\fBTcl_AddErrorInfo\fR, \fBTcl_AddObjErrorInfo\fR,

and \fBTcl_SetErrorCode\fR.

.SH OLD STRING PROCEDURES

.PP

Use of the following procedures is deprecated

since they manipulate the Tcl result as a string.

Procedures such as \fBTcl_SetObjResult\fR

that manipulate the result as an object

can be significantly more efficient.

.PP

\fBTcl_AppendResult\fR makes it easy to build up Tcl results in pieces.

It takes each of its \fIstring\fR arguments and appends them in order

to the current result associated with \fIinterp\fR.

If the result is in its initialized empty state (e.g. a command procedure

was just invoked or \fBTcl_ResetResult\fR was just called),

then \fBTcl_AppendResult\fR sets the result to the concatenation of

its \fIstring\fR arguments.

\fBTcl_AppendResult\fR may be called repeatedly as additional pieces

of the result are produced.

\fBTcl_AppendResult\fR takes care of all the

storage management issues associated with managing \fIinterp\fR's

result, such as allocating a larger result area if necessary.

It also converts the current interpreter result from an object

to a string, if necessary, before appending the argument strings.

Any number of \fIstring\fR arguments may be passed in a single

call; the last argument in the list must be a NULL pointer.

.PP

\fBTcl_AppendElement\fR is similar to \fBTcl_AppendResult\fR in

that it allows results to be built up in pieces.

However, \fBTcl_AppendElement\fR takes only a single \fIstring\fR

argument and it appends that argument to the current result

as a proper Tcl list element.

\fBTcl_AppendElement\fR adds backslashes or braces if necessary

to ensure that \fIinterp\fR's result can be parsed as a list and that

\fIstring\fR will be extracted as a single element.

Under normal conditions, \fBTcl_AppendElement\fR will add a space

character to \fIinterp\fR'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. \fIinterp\fR's current result is empty, or consists of the

single character ``{'', or ends in the characters `` {'') then no

space is added.

.PP

\fBTcl_FreeResult\fR performs part of the work

of \fBTcl_ResetResult\fR.

It frees up the memory associated with \fIinterp\fR's result.

It also sets \fIinterp->freeProc\fR to zero, but doesn't

change \fIinterp->result\fR or clear error state.

\fBTcl_FreeResult\fR is most commonly used when a procedure

is about to replace one result value with another.

.SH DIRECT ACCESS TO INTERP->RESULT IS DEPRECATED

.PP

It used to be legal for programs to

directly read and write \fIinterp->result\fR

to manipulate the interpreter result.

Direct access to \fIinterp->result\fR 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 \fBTcl_GetObjResult\fR or \fBTcl_GetStringResult\fR,

and write the result using \fBTcl_SetObjResult\fR or \fBTcl_SetResult\fR.

.SH THE TCL_FREEPROC ARGUMENT TO TCL_SETRESULT

.PP

\fBTcl_SetResult\fR's \fIfreeProc\fR argument specifies how

the Tcl system is to manage the storage for the \fIstring\fR argument.

If \fBTcl_SetResult\fR or \fBTcl_SetObjResult\fR are called

at a time when \fIinterp\fR holds a string result,

they do whatever is necessary to dispose of the old string result

(see the \fBTcl_Interp\fR manual entry for details on this).

.PP

If \fIfreeProc\fR is \fBTCL_STATIC\fR it means that \fIstring\fR

refers to an area of static storage that is guaranteed not to be

modified until at least the next call to \fBTcl_Eval\fR.

If \fIfreeProc\fR

is \fBTCL_DYNAMIC\fR it means that \fIstring\fR was allocated with a call

to \fBTcl_Alloc\fR and is now the property of the Tcl system.

\fBTcl_SetResult\fR will arrange for the string's storage to be

released by calling \fBTcl_Free\fR when it is no longer needed.

If \fIfreeProc\fR is \fBTCL_VOLATILE\fR it means that \fIstring\fR

points to an area of memory that is likely to be overwritten when

\fBTcl_SetResult\fR returns (e.g. it points to something in a stack frame).

In this case \fBTcl_SetResult\fR 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.

.PP

If \fIfreeProc\fR isn't one of the values \fBTCL_STATIC\fR,

\fBTCL_DYNAMIC\fR, and \fBTCL_VOLATILE\fR, 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 \fIfreeProc\fR. \fIFreeProc\fR should have arguments and

result that match the type \fBTcl_FreeProc\fR:

.CS

typedef void Tcl_FreeProc(char *\fIblockPtr\fR);

.CE

When \fIfreeProc\fR is called, its \fIblockPtr\fR will be set to

the value of \fIstring\fR passed to \fBTcl_SetResult\fR.

.SH "SEE ALSO"

Tcl_AddErrorInfo, Tcl_CreateObjCommand, Tcl_SetErrorCode, Tcl_Interp

.SH KEYWORDS

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