Tcl Library Procedures
Tcl_LinkVar, Tcl_UnlinkVar, Tcl_UpdateLinkedVar - link Tcl variable to C variable
Tcl_LinkVar(interp, varName, addr, type)
Tcl_Interp *interp (in)
Interpreter that contains varName.
Also used by Tcl_LinkVar to return error messages.
char *varName (in)
Name of global variable. Must be in writable memory: Tcl may make
temporary modifications to it while parsing the variable name.
char *addr (in)
Address of C variable that is to be linked to varName.
int type (in)
Type of C variable. Must be one of TCL_LINK_INT, TCL_LINK_DOUBLE,
TCL_LINK_BOOLEAN, or TCL_LINK_STRING, optionally OR'ed with
TCL_LINK_READ_ONLY to make Tcl variable read-only.
Tcl_LinkVar uses variable traces to keep the Tcl variable
named by varName in sync with the C variable at the address
given by addr.
Whenever the Tcl variable is read the value of the C variable will
be returned, and whenever the Tcl variable is written the C
variable will be updated to have the same value.
Tcl_LinkVar normally returns TCL_OK; if an error occurs
while setting up the link (e.g. because varName is the
name of array) then TCL_ERROR is returned and interp->result
contains an error message.
The type argument specifies the type of the C variable,
and must have one of the following values, optionally OR'ed with
The C variable is of type int.
Any value written into the Tcl variable must have a proper integer
form acceptable to Tcl_GetInt; attempts to write
non-integer values into varName will be rejected with
The C variable is of type double.
Any value written into the Tcl variable must have a proper real
form acceptable to Tcl_GetDouble; attempts to write
non-real values into varName will be rejected with
The C variable is of type int.
If its value is zero then it will read from Tcl as ``0'';
otherwise it will read from Tcl as ``1''.
Whenever varName is
modified, the C variable will be set to a 0 or 1 value.
Any value written into the Tcl variable must have a proper boolean
form acceptable to Tcl_GetBoolean; attempts to write
non-boolean values into varName will be rejected with
The C variable is of type char *.
If its value is not null then it must be a pointer to a string
allocated with Tcl_Alloc.
Whenever the Tcl variable is modified the current C string will be
freed and new memory will be allocated to hold a copy of the variable's
If the C variable contains a null pointer then the Tcl variable
will read as ``NULL''.
If the TCL_LINK_READ_ONLY flag is present in type then the
variable will be read-only from Tcl, so that its value can only be
changed by modifying the C variable.
Attempts to write the variable from Tcl will be rejected with errors.
Tcl_UnlinkVar removes the link previously set up for the
variable given by varName. If there does not exist a link
for varName then the procedure has no effect.
Tcl_UpdateLinkedVar may be invoked after the C variable has
changed to force the Tcl variable to be updated immediately.
In many cases this procedure is not needed, since any attempt to
read the Tcl variable will return the latest value of the C variable.
However, if a trace has been set on the Tcl variable (such as a
Tk widget that wishes to display the value of the variable), the
trace will not trigger when the C variable has changed.
Tcl_UpdateLinkedVar ensures that any traces on the Tcl
variable are invoked.
boolean, integer, link, read-only, real, string, traces, variable
Last change: 7.5
[ tcl8.0a1 | tk8.0a1 | X-ref ]
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