1996-06-26 06:06:43 +00:00
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'\"
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'\" Copyright (c) 1993 The Regents of the University of California.
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'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
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'\"
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'\" See the file "license.terms" for information on usage and redistribution
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'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
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'\"
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1996-09-18 14:12:34 +00:00
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'\" SCCS: @(#) LinkVar.3 1.13 96/06/05 18:00:14
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1996-06-26 06:06:43 +00:00
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'\"
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.so man.macros
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.TH Tcl_LinkVar 3 7.5 Tcl "Tcl Library Procedures"
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.BS
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.SH NAME
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Tcl_LinkVar, Tcl_UnlinkVar, Tcl_UpdateLinkedVar \- link Tcl variable to C variable
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.SH SYNOPSIS
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.nf
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\fB#include <tcl.h>\fR
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.sp
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int
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\fBTcl_LinkVar\fR(\fIinterp, varName, addr, type\fR)
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.sp
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\fBTcl_UnlinkVar\fR(\fIinterp, varName\fR)
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.sp
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.VS
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\fBTcl_UpdateLinkedVar\fR(\fIinterp, varName\fR)
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.VE
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.SH ARGUMENTS
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.AS Tcl_Interp writable
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.AP Tcl_Interp *interp in
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Interpreter that contains \fIvarName\fR.
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Also used by \fBTcl_LinkVar\fR to return error messages.
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.AP char *varName in
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Name of global variable.
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.AP char *addr in
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Address of C variable that is to be linked to \fIvarName\fR.
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.AP int type in
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Type of C variable. Must be one of TCL_LINK_INT, TCL_LINK_DOUBLE,
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TCL_LINK_BOOLEAN, or TCL_LINK_STRING, optionally OR'ed with
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TCL_LINK_READ_ONLY to make Tcl variable read-only.
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.BE
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.SH DESCRIPTION
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.PP
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\fBTcl_LinkVar\fR uses variable traces to keep the Tcl variable
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named by \fIvarName\fR in sync with the C variable at the address
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given by \fIaddr\fR.
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Whenever the Tcl variable is read the value of the C variable will
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be returned, and whenever the Tcl variable is written the C
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variable will be updated to have the same value.
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\fBTcl_LinkVar\fR normally returns TCL_OK; if an error occurs
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while setting up the link (e.g. because \fIvarName\fR is the
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name of array) then TCL_ERROR is returned and \fIinterp->result\fR
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contains an error message.
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.PP
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The \fItype\fR argument specifies the type of the C variable,
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and must have one of the following values, optionally OR'ed with
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TCL_LINK_READ_ONLY:
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.TP
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\fBTCL_LINK_INT\fR
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The C variable is of type \fBint\fR.
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Any value written into the Tcl variable must have a proper integer
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form acceptable to \fBTcl_GetInt\fR; attempts to write
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non-integer values into \fIvarName\fR will be rejected with
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Tcl errors.
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.TP
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\fBTCL_LINK_DOUBLE\fR
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The C variable is of type \fBdouble\fR.
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Any value written into the Tcl variable must have a proper real
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form acceptable to \fBTcl_GetDouble\fR; attempts to write
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non-real values into \fIvarName\fR will be rejected with
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Tcl errors.
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.TP
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\fBTCL_LINK_BOOLEAN\fR
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The C variable is of type \fBint\fR.
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If its value is zero then it will read from Tcl as ``0'';
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otherwise it will read from Tcl as ``1''.
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Whenever \fIvarName\fR is
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modified, the C variable will be set to a 0 or 1 value.
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Any value written into the Tcl variable must have a proper boolean
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form acceptable to \fBTcl_GetBoolean\fR; attempts to write
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non-boolean values into \fIvarName\fR will be rejected with
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Tcl errors.
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.TP
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\fBTCL_LINK_STRING\fR
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The C variable is of type \fBchar *\fR.
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1996-09-18 14:12:34 +00:00
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.VS
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1996-06-26 06:06:43 +00:00
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If its value is not null then it must be a pointer to a string
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1996-09-18 14:12:34 +00:00
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allocated with \fBTcl_Alloc\fR.
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.VE
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1996-06-26 06:06:43 +00:00
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Whenever the Tcl variable is modified the current C string will be
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freed and new memory will be allocated to hold a copy of the variable's
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new value.
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If the C variable contains a null pointer then the Tcl variable
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will read as ``NULL''.
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.PP
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If the TCL_LINK_READ_ONLY flag is present in \fItype\fR then the
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variable will be read-only from Tcl, so that its value can only be
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changed by modifying the C variable.
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Attempts to write the variable from Tcl will be rejected with errors.
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.PP
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\fBTcl_UnlinkVar\fR removes the link previously set up for the
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variable given by \fIvarName\fR. If there does not exist a link
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for \fIvarName\fR then the procedure has no effect.
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.PP
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.VS
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\fBTcl_UpdateLinkedVar\fR may be invoked after the C variable has
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changed to force the Tcl variable to be updated immediately.
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In many cases this procedure is not needed, since any attempt to
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read the Tcl variable will return the latest value of the C variable.
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However, if a trace has been set on the Tcl variable (such as a
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Tk widget that wishes to display the value of the variable), the
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trace will not trigger when the C variable has changed.
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\fBTcl_UpdateLinkedVar\fR ensures that any traces on the Tcl
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variable are invoked.
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.VE
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.SH KEYWORDS
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boolean, integer, link, read-only, real, string, traces, variable
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