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Tk_CreateSelHandler(3)                      Tk Library Procedures                     Tk_CreateSelHandler(3)



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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 for-mat format
                                                 mat 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 selec-tion selection
                                                 tion 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  Con-ventions Conventions
       ventions  Manual  (ICCCM)  or any other form in which an application is willing to present the selec-tion. selection.
       tion.  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 thou-sand thousand
       sand 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 argu-ment argument
       ment  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(3)