[Brass]

Please forgive me if this is a stupid question, but it's many years (back to Uni) since I've done anything in the C language. I'm trying to re-learn it, and got one of my old Uni projects which uses X11 (X-Windows). I cannot get it to link successfully. When I enter "cc <progname.c>" I get the following output:

/usr/bin/ld: Undefined symbols:
_XCreateColormap
_XCreateSimpleWindow
_XDrawPoint
_XFlush
_XMapRaised
_XNextEvent
_XOpenDisplay
_XResizeWindow
_XSelectInput
_XSetForeground
_XSetWindowColormap
_XStoreColor

Yes, I do have X11 installed correctly (using XDarwin and OroborOSX). And I know that it's found the required Xlib.h library header, because before I created a link to the Xfree86 library in /usr/include I got a completely different error (couldn't find the library). Also, I'm getting much the same error with the same source code on the Solaris box here too, and I know that's set up correctly.

Can somebody help me get over this hump on the road to re-learning Unix/C programming?

[ 04-19-2002: Message edited by: Brass ]

[davechen]

Are you linking with the X11 library properly?

your link line should look something like:

cc -o program program.c -L/usr/X11R6/lib -lX11


Those symbols are in the file /usr/X11R6/lib/libX11.a

[Brass]

Aha! It works (or at least, it compiles - causes X-Windows errors when it runs *sigh*)

Thanks for your help. I'm so out of touch with all this now. I need to look up some info on program linking, I guess. There's nothing on it at all in the C textbook I'm using - just the C language, itself. I guess I can use "man cc" and "man ld". I can't even remember what the -L and -l are for.

[davechen]

Yeah, you always have to make sure you include the right libraries in the right order when you link.

The "-Ldirectory" flag says add "directory" to the library path, so it can find the library. The "-llibrary" says link with the file liblibrary.a or liblibrary.dylib (on Macs). On most Unixes, dynamic libraries are .so, not .dylib.

About link order, if you have two libraries, libfoo.a and libbar.a, and libfoo depends on libbar, libfoo should come first on the link line, then libbar. I.e.

cc -o program program.c -lfoo -lbar

dave