CrtSelHdlr man page on DigitalUNIX

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Tk_CreateSelHandler(3)	     Tk Library Procedures	Tk_CreateSelHandler(3)

______________________________________________________________________________

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  informa‐
						 tion.

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

       Atom		  target       (in)	 Form in which proc  can  pro‐
						 vide	the   selection	 (e.g.
						 STRING or FILE_NAME).	Corre‐
						 sponds	 to  type arguments in
						 selection commands.

       Tk_SelectionProc	  *proc	       (in)	 Procedure to invoke  whenever
						 the  selection	 is  owned  by
						 tkwin and the selection  con‐
						 tents	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
						 isn't in this process, format
						 determines the representation
						 used to transmit  the	selec‐
						 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  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_Selection‐
       Proc:
	      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 avail‐
       able 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  charac‐
       ters 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	trans‐
       mission.	 It will do this by calling proc one or more times, using suc‐
       cessively 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 infor‐
       mation 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 mid‐
       dle  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	selec‐
       tion 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)
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