Why I can't get X Display handle?

I call XOpenDisplay to connect to the X server but get a NULL pointer. My client program run in the text terminal, not GUI desktop. I have got the MIT key using the xauth and set the enviroment variable DISPLAY to “localhost/unix:0”.

I have test our program on Ubuntu, Debian and SLE10-sp2, it’s ok. So I am confused. My openSUSE is 11.1.