Tcl_LinkVar
Section: Tcl Library Procedures (3)
Updated: 7.5
Page Index
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. Incomplete integer representations (like the empty
string, '+', '-' or the hex/octal/binary prefix) are accepted
as if they are valid too.
- 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. Incomplete integer
representations (like the empty string, '+', '-' or the hex/octal/binary
prefix) are accepted as if they are valid too.
- 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. Incomplete
integer representations (like the empty string, '+', '-' or the
hex/octal/binary prefix) are accepted as if they are valid too.
- 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. Incomplete integer
representations (like the empty string, '+', '-' or the hex/octal/binary
prefix) are accepted as if they are valid too.
- 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. Incomplete
integer representations (like the empty string, '+', '-' or the
hex/octal/binary prefix) are accepted as if they are valid too.
- 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. Incomplete integer
representations (like the empty string, '+', '-' or the hex/octal/binary
prefix) are accepted as if they are valid too.
- 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. Incomplete
integer representations (like the empty string, '+', '-' or the
hex/octal/binary prefix) are accepted as if they are valid too.
- 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. Incomplete integer
representations (like the empty string, '+', '-' or the hex/octal/binary
prefix) are accepted as if they are valid too.
- 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. Incomplete integer or real representations (like the
empty string, '.', '+', '-' or the hex/octal/binary prefix) are
accepted as if they are valid too.
- 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. Incomplete integer
or real representations (like the empty string, '.', '+', '-' or
the hex/octal/binary prefix) are accepted as if they are valid too.
- 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. Incomplete integer representations (like the empty
string, '+', '-' or the hex/octal/binary prefix) are accepted
as if they are valid too.
- 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. Incomplete integer representations (like
the empty string, '+', '-' or the hex/octal/binary prefix) are accepted
as if they are valid too.
- 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(3)
KEYWORDS
boolean, integer, link, read-only, real, string, trace, variable