A transfer procedure has the same function prototype as any Motif callback. Motif passes the transfer procedure an XmSelectionCallbackStruct pointer as the client_data argument. The targets member of this callback structure holds the name of the target converted by the source widget. For example, TransferProc calls XmTransferValue as follows to request a particular target:

XmTransferValue(ss -> transfer_id, target,
                (XtCallbackProc) TransferProc, NULL, 0);

When the source widget finishes the conversion, UTM calls TransferProc again.

When the source widget finishes converting the desired target, TransferProc must paste the text into the ExmStringTransfer widget. To simplify things, TransferProc overwrites whatever text was previously displayed. For more sophisticated widgets, you will have to determine how to insert the transferred text without overriding the previous text.

ExmStringTransfer displays the contents of the ExmNcompoundString resource. This resource holds an XmString value. Therefore, TransferProc must take the text that the source widget transferred and convert it into XmString format. If the source widget transferred the text as an _MOTIF_COMPOUND_STRING target, then TransferProc will have an easy time converting to XmString. If the source widget has transferred the text as some other target, then the conversion will be more difficult. For example, the following code from TransferProc handles the situation where the source widget transferred the text as COMPOUND_TEXT:

if (ss -> type == COMPOUND_TEXT) {
    /* Convert compound text to a compound string.
     * Note that XmCvtCTToXmString does not convert a list of compound
text
     * strings, so we will get only the first if there's more than one.
     * XmCvtCTToXmString expects a NULL-terminated compound text string,
     * so add a trailing NULL. */
    char *string;
    string = XtMalloc(ss -> length + 1);
   (void) memcpy(string, ss -> value, ss -> length);
    string[ss -> length] = ' ';
    cstring = XmCvtCTToXmString(string);
    XtFree(string);
    transferred = True;
}

TransferProc contains similar code that converts text in other targets to XmString format. Eventually, TransferProc uses XtSetValues to assign the transferred XmString to the ExmNcompoundString resource as follows:

if (transferred) {
    /* We have a compound string. Use it as the new value of
     * ExmNcompoundString. */
    Arg args[1];
    Cardinal n;
    n = 0;
    XtSetArg(args[n], ExmNcompoundString, cstring);  n++;
    XtSetValues(w, args, n);
}

If the locale atom is not present, PreferredTargets uses this order:

The code in PreferredTarget that implements the precedence is as follows:

static Atom
PreferredTarget(
     Widget w,
     Atom *targets,
     Cardinal num_targets)
{
  ...
  int n;
  int cs_index = -1;
  int ct_index = -1;
  int locale_index = -1;
  int string_index = -1;
  int text_index = -1;
 /* Which targets can the source convert? Examine the returned targets.
*/
  for (n = 0; n < num_targets; n++) {
    if (targets[n] == MOTIF_C_S) cs_index = n;
    if (targets[n] == COMPOUND_TEXT) ct_index = n;
    if (targets[n] == TEXT) text_index = n;
    if (targets[n] == LOCALE_ATOM) locale_index = n;
    if (targets[n] == XA_STRING) string_index = n;
  }
 
 /* If the source supports the locale atom, specify the
    precedence order as follows. */
  if (locale_index >= 0) {
    if (cs_index >= 0) return targets[cs_index];
    if (text_index >= 0) return targets[text_index];
    if (ct_index >= 0) return targets[ct_index];
    if (locale_index >= 0) return targets[locale_index];
    if (string_index >= 0) return targets[string_index];
  } else {
 /* If the source does not support the locale atom, specify the
    precedence order as follows. */
    if (cs_index >= 0) return targets[cs_index];
    if (ct_index >= 0) return targets[ct_index];
    if (string_index >= 0) return targets[string_index];
  }
 
  return None;
}