pointers - Lisp, cffi, let and memory -

i've build toy c++ library create qt window lisp. know common-qt exists, i'm trying learn how use cffi.

right now, have 4 binded functions :

• create-application : create qapplication , return pointer
• create-window : create qmainwindow , return poiner
• show : show window specified argument
• exec : qt exec function

here lisp code work :

(defctype t-app :pointer) (defctype t-window :pointer)  (defcfun (create-application "create_application" ) t-app) (defcfun (exec "exec") :void (app t-app)) (defcfun (create-window-aalt "create_window_aalt") t-window) (defcfun (show "show") :void (o t-window))  (defparameter (create-application)) (defparameter w (create-window-aalt)) (show w) (exec a) 

but if use let or let*...i have memory fault !

(let* ((a (create-application)) (w (create-window-aalt)))     (show w)     (exec a))   corruption warning in sbcl pid 1312(tid 140737353860992): memory fault @ a556508 (pc=0x7ffff659b7f1, sp=0x7ffff2bbe688) integrity of image possibly compromised. exiting. 

does know why ?

i using sbcl :

env ld_library_path=`pwd` \ env ld_preload=/usr/lib/libqtgui.so.4 \ sbcl --script aalt.lisp 

thanks.

i suggest following:

1. since writing library c++ , using symbols lisp, make sure use extern "c" declarations - needed ensure c++ compiler not mangle names.

2. check library works in c (not c++) application. ensure library working (e.g., not throw c++ exceptions).

upd:

i've tried run code , had same crash. problem seems in create_application function. i've attached fixed version of function @ http://paste.lisp.org/display/138049.

concretely, there 2 problems:

1. create_application allocated v on stack. subsequent code (i.e., let binding) overwrites it.

2. argv should null-terminated. i.e., should contain argc+1 elements - last element null. (qt seems not use this, habit write code according specs).

in case, stack allocation problem - seems let binding overwrites value of v on stack, crashing sbcl. using malloc or new allocate argv on heap fixes issue.