NAME¶
Tcl_LinkVar, Tcl_UnlinkVar, Tcl_UpdateLinkedVar - link Tcl variable to C
variable
SYNOPSIS¶
#include <tcl.h>
int
Tcl_LinkVar(interp, varName, addr, type)
Tcl_UnlinkVar(interp, varName)
Tcl_UpdateLinkedVar(interp, varName)
ARGUMENTS¶
- 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.
DESCRIPTION¶
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 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:
- TCL_LINK_INT
- 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.
- TCL_LINK_DOUBLE
- 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.
- TCL_LINK_WIDE_INT
- 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 variable must have a proper integer form
acceptable to Tcl_GetWideIntFromObj; attempts to write non-integer
values into varName will be rejected with Tcl errors.
- TCL_LINK_BOOLEAN
- 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.
- TCL_LINK_STRING
- 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 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.
KEYWORDS¶
boolean, integer, link, read-only, real, string, traces, variable