How to clear/replace filter list in File Chooser?

[Toralf Lund <toralf procaptura com>]

Does anyone here know how to clear the list of user selectable filters 
from a file selector and/or replace the list with a new one? Or 
differently put, can someone spot the mistake(s) in the code included below?

What I want to do, is to set up a file chooser that has exactly two 
filters at any given time - one that allows selection of any file, and 
one that matches files based on a given list of extensions. This set of 
extensions may change between each time the file chooser is used (based 
on configuration of other parts of the GUI), so I may need to reset and 
set the filter list several times throughout the lifetime of the 
FileChooser object. (The same chooser for multiple file open operations.)

To be able to do this, I've written the following method (in a class 
derived from FileChooserDialog.) The problem is, it doesn't quite work. 
It is OK the first time around, but if I call it again in order to 
change the extension list, the program dumps core.

So, can anyone tell me what is wrong here?

Oh, and before anyone suggests it: I realise that I might "fix" the 
problem by creating a new FileChooserDialog every time instead of trying 
to reuse the same, of course, but I'd really like to know why exactly 
the below approach fails.

void FileSelection::setValidExtensions(const std::vector<std::string> &validExtensions, const std::string &filterId)
{
 std::vector<const Gtk::FileFilter*> filters=list_filters();
 for(std::vector<const Gtk::FileFilter*>::iterator f=filters.begin(); 
     f!=filters.end(); f++) {
   remove_filter(*(*f));
 }
 
 Gtk::FileFilter allFilter;

 allFilter.add_pattern("*");
 allFilter.set_name("All Files");

 add_filter(allFilter);
 
 if(!validExtensions.empty()) {
   Gtk::FileFilter extFilter;
   std::string extName="All valid (";
   
   for(std::vector<std::string>::const_iterator p=validExtensions.begin();
	p!=validExtensions.end(); p++) {
     if(!p->empty()) {
	std::string pattern="*";
	if((*p)[0]!='.')
	  pattern+=".";
	pattern+=*p;
	extFilter.add_pattern(pattern);
	
	extName+=pattern;
	extName+=",";
     }
   }
   *extName.rbegin()=')';	// Replace ',' after last item with ')'

   if(filterId.empty())
     extFilter.set_name(extName);
   else
     extFilter.set_name(filterId);
   add_filter(extFilter);
   
   set_filter(extFilter);
 }
}