[vbox-dev] IFramebuffer.GetAddress

[一生有你]

Hi,guys!
  framebuffer->vtbl->GetAddress(framebuffer,&adr) always returns with 0x8000ffff ,it means
  an unknow excption in xpcom. 
  i want to know why it could be this?
 thanks a lot....
  /////////////////////////////here is the code
  IFramebuffer* framebuffer;
 int xo,yo;
 rc=display->vtbl->GetFramebuffer(display,0,&framebuffer,&xo,&yo);
 if(NS_SUCCEEDED(rc)) printf("framebuffer exist\n");//realy exist...
 
 unsigned int fw,fh,fbpp;
 framebuffer->vtbl->GetWidth(framebuffer,&fw);
 framebuffer->vtbl->GetHeight(framebuffer,&fh);
 framebuffer->vtbl->GetBitsPerPixel(framebuffer,&fbpp);
 printf("framebuffer   Width: %u Height: %u Bits Per Pixel: %u \n ",fw,fh,bpp);
 //printf outputs the correct  Width Height and Bits Per Pixel......but getaddress fails....
 
 unsigned char* adr;
  rc=framebuffer->vtbl->GetAddress(framebuffer,&adr);
 if(NS_SUCCEEDED(rc)) ////////fails here ???why 
 printf(">>>>>>>>>>>>>>>>%p.......\n",adr);
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