OpenEuphoria

1. EuGTK - Segmentation fault, GtkCheckMenuItem

• Posted by Jerry_Story Oct 19, 2010
• 1117 views

What causes the segmentation fault?

global procedure setReqs(integer r) 
atom ctl 
 
-- r is getting correct numbers. 
 
  for i = 1 to length(MenuReqs) do 
    set(MenuReqs[i],"active",0) 
  end for 
-- Each MenuReqs[i] is a GtkCheckMenuItem. 
-- All these show up in the menu bar and are clickable. 
 
  ctl = MenuReqs[r] 
 
printf(1,"after ctl  ctl=%d \n",{ctl}) --  (1) 
-- This prints a large number, as it should. 
-- But this line is executed many times, (2) below never. How? 
-- ctl is the same number each time. 
 
  set(ctl,"active",1) 
-- Segmentation fault happens here. 
-- When I comment this statement out, the segmentation fault does not happen. 
-- set(ctl,"active",TRUE) makes no difference. 
 
printf(1,"after ctl 1  r=%d \n\n",{r}) -- (2) 
-- It never gets here. 
-- How can line (1) be executed many times and line (2) never? 
 
-- more code 
 
end procedure  -- setReqs() 

This is what happens.

after ctl  ctl=327386248  
after ctl  ctl=327386248  
after ctl  ctl=327386248  
after ctl  ctl=327386248  
after ctl  ctl=327386248  
after ctl  ctl=327386248  
after ctl  ctl=327386248  
after ctl  ctl=327386248  
after ctl  ctl=327386248  
... etc ... 
Segmentation fault 

I've been hung up on this bug for days with zero progress. How can I make some progress with this bug?

3. Re: EuGTK - Segmentation fault, GtkCheckMenuItem

• Posted by Jerry_Story Oct 19, 2010
• 1120 views

integer setting=0 
global procedure setReqs(integer r) 
atom ctl 
 
  if not setting then 
    setting = 1 
    for i = 1 to length(MenuReqs) do 
      set(MenuReqs[i],"active",0) 
    end for 
 
    ctl = MenuReqs[r] 
 
    set(ctl,"active",1) 
 
    setting = 0 
  end if 
end procedure  -- setReqs() 

    for i = 1 to length(MenuReqs) do 
      if i!=r then 
        set(MenuReqs[i],"active",0) 
      end if 
    end for 

The first one stops the segmentation fault. But how can set(), part of EuGTK, call setReqs()?

The second one goes into an endless loop without the segmentation fault, and alternating between 2 numbers.

after ctl 1  r=3  
 
after ctl  ctl=170814224  
after ctl  ctl=170814224  
after ctl  ctl=170814224  
after ctl 1  r=2  
 
after ctl 1  r=2  
 
after ctl  ctl=331504664  
after ctl  ctl=331504664  
after ctl  ctl=331504664  
after ctl 1  r=3  
 
after ctl 1  r=3  
 
after ctl  ctl=170814224  
after ctl  ctl=170814224  
after ctl  ctl=170814224  
after ctl 1  r=2  
 
after ctl 1  r=2  

5. Re: EuGTK - Segmentation fault, GtkCheckMenuItem

• Posted by irv Oct 19, 2010
• 1036 views

Hmm... let me rephrase that so it's clearer:

When you toggle a check button from active to inactive, or vice-versa, it's the same as clicking on it to change the state.

So, if you have connected any signal to that button so that it responds to changes in state, that routine (or any routine it calls) can't also change the state, else your routine will just sit there in a loop.

Here's a simple demo:

include GtkEngine.e 
 
function Foo(atom x) 
? x 
set(x,"active",0) 
set(x,"active",1) 
return 1 
end function 
 
load_xml(builder,"cktest1.glade") 
connect("window1","destroy",quit) 
 
connect("checkbutton1","clicked",call_back(routine_id("Foo"))) 
 
show_all("window1") 
main() 

The above code will loop until you get a seg fault. Note that it isn't necessary to directly call the offending routine from the connect signal. You may be connecting to some other function that calls the endless loop proc().

BTW, it's normally not a good idea to connect any action to clicking on a check button/box. Suppose the page has 2 or more check items. Do you really want to go do something each time one is clicked, or do you want to wait until the user has finished and has them all set the way he wants? IOW, set up the check buttons/boxes, etc, and then put an OK button to be clicked when the selections are finished.

If you feel you MUST do something the moment a checkbox is clicked, then use the "pressed" or "released" signal rather than the "clicked" signal. This way, you won't get into an endless loop, 'cause your response will be to a mouse action rather than a state change. This works well for a checkmenu item.

However, looking at your code, I wonder if you are trying to use checkmenuitems as radiomenuitems - turning off all the others when one is clicked?