trusty (3) Tcl_LinkVar.3tcl.gz

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