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