NAME

       Tk_CreateSelHandler, Tk_DeleteSelHandler - arrange to handle requests for a selection

SYNOPSIS

       #include <tk.h>

       Tk_CreateSelHandler(tkwin, selection, target, proc, clientData, format)

       Tk_DeleteSelHandler(tkwin, selection, target)

ARGUMENTS

       Tk_Window tkwin (in)                      Window for which proc will provide selection information.

       Atom selection (in)                       The name of the selection for which proc will provide selection
                                                 information.

       Atom target (in)                          Form  in  which  proc can provide the selection (e.g. STRING or
                                                 FILE_NAME).   Corresponds  to  type  arguments   in   selection
                                                 commands.

       Tk_SelectionProc *proc (in)               Procedure  to  invoke  whenever the selection is owned by tkwin
                                                 and the selection contents are requested in the format given by
                                                 target.

       ClientData clientData (in)                Arbitrary one-word value to pass to proc.

       Atom format (in)                          If the selection requestor  is  not  in  this  process,  format
                                                 determines the representation used to transmit the selection to
                                                 its requestor.
________________________________________________________________________________________________________________

DESCRIPTION

       Tk_CreateSelHandler  arranges  for a particular procedure (proc) to be called whenever selection is owned
       by tkwin and the selection contents are requested in the form given by target.  Target should be  one  of
       the  entries defined in the left column of Table 2 of the X Inter-Client Communication Conventions Manual
       (ICCCM) or any other form in which an application is willing to present the selection.  The  most  common
       form is STRING.

       Proc should have arguments and result that match the type Tk_SelectionProc:
              typedef int Tk_SelectionProc(
                      ClientData clientData,
                      int offset,
                      char *buffer,
                      int maxBytes);
       The  clientData  parameter  to  proc  is  a copy of the clientData argument given to Tk_CreateSelHandler.
       Typically, clientData points to a data structure  containing  application-specific  information  that  is
       needed  to  retrieve  the  selection.   Offset  specifies  an  offset position into the selection, buffer
       specifies a location at which to copy information about the selection, and maxBytes specifies the  amount
       of  space  available at buffer.  Proc should place a NULL-terminated string at buffer containing maxBytes
       or fewer characters (not including the terminating NULL), and it should return a count of the  number  of
       non-NULL  characters  stored  at buffer.  If the selection no longer exists (e.g. it once existed but the
       user deleted the range of characters containing it), then proc should return -1.

       When transferring large selections, Tk will break them up into smaller pieces (typically a  few  thousand
       bytes  each)  for  more efficient transmission.  It will do this by calling proc one or more times, using
       successively higher values of offset to retrieve successive portions of the selection.  If proc returns a
       count less than maxBytes it means that the entire remainder of  the  selection  has  been  returned.   If
       proc's return value is maxBytes it means there may be additional information in the selection, so Tk must
       make another call to proc to retrieve the next portion.

       Proc  always  returns selection information in the form of a character string.  However, the ICCCM allows
       for information to be transmitted from the selection owner to the selection requestor in any  of  several
       formats,  such  as  a  string,  an  array  of  atoms,  an array of integers, etc.  The format argument to
       Tk_CreateSelHandler indicates what format should be used to transmit the selection to its requestor  (see
       the  middle column of Table 2 of the ICCCM for examples).  If format is not STRING, then Tk will take the
       value returned by proc and divided it into fields separated by white space.  If format is ATOM,  then  Tk
       will  return  the selection as an array of atoms, with each field in proc's result treated as the name of
       one atom.  For any other value of format, Tk will return the selection as an array of 32-bit values where
       each field of proc's result is treated as a number and translated to a 32-bit value.  In any  event,  the
       format atom is returned to the selection requestor along with the contents of the selection.

       If  Tk_CreateSelHandler  is called when there already exists a handler for selection and target on tkwin,
       then the existing handler is replaced with a new one.

       Tk_DeleteSelHandler removes the handler given by tkwin, selection, and target, if such a handler  exists.
       If there is no such handler then it has no effect.

KEYWORDS

       format, handler, selection, target

Tk                                                     4.0                              Tk_CreateSelHandler(3tk)