How do I use global variables from one dll in another (not multi-threaded)

[pblase]

Using LabWindows/CVI. I'm trying to be compatible with legacy code, so this isn't the best way to do things but it saves me some headaches.

I have one project/.dll called "GlobalBlock" that contains certain parameters used widely throughout the program. The whole program consists of multiple dlls, for encapsulation purposes.

GlobalBlock.c contains:

struct menu_sdef G_setprefs =
{
//... stuff

};

struct sys_fileheader_sdef Level1Version =
{
//... more stuff

};

struct sys_flags_sdef G_sys_flags;

[pblase]

Sorry, hit the wrong button.

GlobalBlock.h contains:

   #ifndef __GlobalBlock_C__
    extern struct menu_sdef              G_setprefs;
    extern struct sys_fileheader_sdef Level1Version;
    extern struct sys_flags_sdef        G_sys_flags;
 
   ...

   #endif

When I compile the second dll, Plots.c, the C code for which contains something like

   #include "GlobalBlock.h"

... 

G_setprefs.X = 1.23;

I get :

"undefined symbol '_G_setprefs' in Plots.c

"undefined symbol '_G_sys_flags' in Plots.c

The Build option to include the .h file in the library is set. 

I've searched the forums and the help files, and can't find any indication that I should be doing anything different.

[jr_2005 · Accepted solution]

In the dll that owns the variable, use the _export qualifier on it. This will ensure that it is placed in the dll interface list. In the application (dll or otherwise) that wants to reference this variable, use the _import qualifier on it. This tells the system to use the associated import library that comes with the dll, in order to resolve the references at run time.

JR

[pblase]

Thanks much.

Paul