source: downloads/tcl8.5.2/doc/BoolObj.3 @ 35

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'\" Copyright (c) 1996-1997 Sun Microsystems, Inc.
'\" Contributions from Don Porter, NIST, 2005.  (not subject to US copyright)
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'\" RCS: @(#) $Id: BoolObj.3,v 1.11 2007/12/13 15:22:30 dgp Exp $
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.so man.macros
.TH Tcl_BooleanObj 3 8.5 Tcl "Tcl Library Procedures"
.BS
.SH NAME
Tcl_NewBooleanObj, Tcl_SetBooleanObj, Tcl_GetBooleanFromObj \- store/retrieve boolean value in a Tcl_Obj
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
Tcl_Obj *
\fBTcl_NewBooleanObj\fR(\fIboolValue\fR)
.sp
\fBTcl_SetBooleanObj\fR(\fIobjPtr, boolValue\fR)
.sp
int
\fBTcl_GetBooleanFromObj\fR(\fIinterp, objPtr, boolPtr\fR)
.SH ARGUMENTS
.AS Tcl_Interp boolValue in/out
.AP int boolValue in
Integer value to be stored as a boolean value in a Tcl_Obj.
.AP Tcl_Obj *objPtr in/out
Points to the Tcl_Obj in which to store, or from which to
retrieve a boolean value.
.AP Tcl_Interp *interp in/out
If a boolean value cannot be retrieved,
an error message is left in the interpreter's result object
unless \fIinterp\fR is NULL.
.AP int *boolPtr out
Points to place where \fBTcl_GetBooleanFromObj\fR
stores the boolean value (0 or 1) obtained from \fIobjPtr\fR.
.BE

.SH DESCRIPTION
.PP
These procedures are used to pass boolean values to and from
Tcl as Tcl_Obj's.  When storing a boolean value into a Tcl_Obj,
any non-zero integer value in \fIboolValue\fR is taken to be
the boolean value \fB1\fR, and the integer value \fB0\fR is
taken to be the boolean value \fB0\fR.
.PP
\fBTcl_NewBooleanObj\fR creates a new Tcl_Obj, stores the boolean
value \fIboolValue\fR in it, and returns a pointer to the new Tcl_Obj.
The new Tcl_Obj has reference count of zero.
.PP
\fBTcl_SetBooleanObj\fR accepts \fIobjPtr\fR, a pointer to
an existing Tcl_Obj, and stores in the Tcl_Obj \fI*objPtr\fR 
the boolean value \fIboolValue\fR.  This is a write operation
on \fI*objPtr\fR, so \fIobjPtr\fR must be unshared.  Attempts to
write to a shared Tcl_Obj will panic.  A successful write
of \fIboolValue\fR into \fI*objPtr\fR implies the freeing of
any former value stored in \fI*objPtr\fR.
.PP
\fBTcl_GetBooleanFromObj\fR attempts to retrive a boolean value
from the value stored in \fI*objPtr\fR.
If \fIobjPtr\fR holds a string value recognized by \fBTcl_GetBoolean\fR,
then the recognized boolean value is written at the address given
by \fIboolPtr\fR.  
If \fIobjPtr\fR holds any value recognized as
a number by Tcl, then if that value is zero a 0 is written at
the address given by \fIboolPtr\fR and if that
value is non-zero a 1 is written at the address given by \fIboolPtr\fR.
In all cases where a value is written at the address given
by \fIboolPtr\fR, \fBTcl_GetBooleanFromObj\fR returns \fBTCL_OK\fR.
If the value of \fIobjPtr\fR does not meet any of the conditions
above, then \fBTCL_ERROR\fR is returned and an error message is 
left in the interpreter's result unless \fIinterp\fR is NULL.
\fBTcl_GetBooleanFromObj\fR may also make changes to the internal
fields of \fI*objPtr\fR so that future calls to 
\fBTcl_GetBooleanFromObj\fR on the same \fIobjPtr\fR can be
performed more efficiently.
.PP
Note that the routines \fBTcl_GetBooleanFromObj\fR and
\fBTcl_GetBoolean\fR are not functional equivalents.
The set of values for which \fBTcl_GetBooleanFromObj\fR
will return \fBTCL_OK\fR is strictly larger than
the set of values for which \fBTcl_GetBoolean\fR will do the same.
For example, the value
.QW 5
passed to \fBTcl_GetBooleanFromObj\fR
will lead to a \fBTCL_OK\fR return (and the boolean value 1),
while the same value passed to \fBTcl_GetBoolean\fR will lead to
a \fBTCL_ERROR\fR return.

.SH "SEE ALSO"
Tcl_NewObj, Tcl_IsShared, Tcl_GetBoolean

.SH KEYWORDS
boolean, object