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_UINT, TCL_LINK_CHAR, TCL_LINK_UCHAR,
TCL_LINK_SHORT, TCL_LINK_USHORT, TCL_LINK_LONG,
TCL_LINK_ULONG, TCL_LINK_WIDE_INT,
TCL_LINK_WIDE_UINT, TCL_LINK_FLOAT, TCL_LINK_DOUBLE,
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_UINT
- The C variable is of type unsigned int. Any value written into the
Tcl variable must have a proper unsigned integer form acceptable to
Tcl_GetWideIntFromObj and in the platform's defined range for the
unsigned int type; attempts to write non-integer values (or values
outside the range) into varName will be rejected with Tcl
errors.
- TCL_LINK_CHAR
- The C variable is of type char. Any value written into the Tcl
variable must have a proper integer form acceptable to
Tcl_GetIntFromObj and be in the range of the char datatype;
attempts to write non-integer or out-of-range values into varName
will be rejected with Tcl errors.
- TCL_LINK_UCHAR
- The C variable is of type unsigned char. Any value written into the
Tcl variable must have a proper unsigned integer form acceptable to
Tcl_GetIntFromObj and in the platform's defined range for the
unsigned char type; attempts to write non-integer values (or values
outside the range) into varName will be rejected with Tcl
errors.
- TCL_LINK_SHORT
- The C variable is of type short. Any value written into the Tcl
variable must have a proper integer form acceptable to
Tcl_GetIntFromObj and be in the range of the short datatype;
attempts to write non-integer or out-of-range values into varName
will be rejected with Tcl errors.
- TCL_LINK_USHORT
- The C variable is of type unsigned short. Any value written into
the Tcl variable must have a proper unsigned integer form acceptable to
Tcl_GetIntFromObj and in the platform's defined range for the
unsigned short type; attempts to write non-integer values (or
values outside the range) into varName will be rejected with Tcl
errors.
- TCL_LINK_LONG
- The C variable is of type long. Any value written into the Tcl
variable must have a proper integer form acceptable to
Tcl_GetLongFromObj; attempts to write non-integer or out-of-range
values into varName will be rejected with Tcl errors.
- TCL_LINK_ULONG
- The C variable is of type unsigned long. Any value written into the
Tcl variable must have a proper unsigned integer form acceptable to
Tcl_GetWideIntFromObj and in the platform's defined range for the
unsigned long type; attempts to write non-integer values (or values
outside the range) 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_FLOAT
- The C variable is of type float. Any value written into the Tcl
variable must have a proper real form acceptable to
Tcl_GetDoubleFromObj and must be within the range acceptable for a
float; attempts to write non-real values (or values outside the
range) 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_WIDE_UINT
- The C variable is of type Tcl_WideUInt (which is an unsigned
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 unsigned
integer form acceptable to Tcl_GetWideIntFromObj (it will be cast
to unsigned); 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.
Note that, as with any call to a Tcl interpreter,
Tcl_UpdateLinkedVar
must be called from the same thread that created the interpreter. The safest
mechanism is to ensure that the C variable is only ever updated from the same
thread that created the interpreter (possibly in response to an event posted
with
Tcl_ThreadQueueEvent), but when it is necessary to update the
variable in a separate thread, it is advised that
Tcl_AsyncMark be used
to indicate to the thread hosting the interpreter that it is ready to run
Tcl_UpdateLinkedVar.
SEE ALSO¶
Tcl_TraceVar(3tcl)
KEYWORDS¶
boolean, integer, link, read-only, real, string, trace, variable