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