Tcl_LinkVar(3) Tcl Library Procedures Tcl_LinkVar(3)
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.
CONST char *varName (in) Name of global variable.
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_WIDE_INT, 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 vari-
able 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 the interpreter's 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 TCL_LINK_READ_ONLY:
The C variable is of type int. Any value written into the Tcl variable must have a
proper integer form acceptable to Tcl_GetIntFromObj; attempts to write non-integer
values into varName will be rejected with Tcl errors.
The C variable is of type double. Any value written into the Tcl variable must
have a proper real form acceptable to Tcl_GetDoubleFromObj; attempts to write non-
real values into varName will be rejected with Tcl errors.
The C variable is of type Tcl_WideInt (which is an integer type at least 64-bits |
wide on all platforms that can support it.) Any value written into the Tcl vari- |
able must have a proper integer form acceptable to Tcl_GetWideIntFromObj; attempts |
to write non-integer values into varName will be rejected with Tcl errors.
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_GetBooleanFromObj; attempts to
write non-boolean values into varName will be rejected with Tcl errors.
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 or ckalloc. 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 new value. 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 vari-
able 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
Tcl 7.5 Tcl_LinkVar(3)