Dynamic-linked DLL needs to share a global variable with its caller.

Question

I have a static library libStatic that defines a global variable like this

Header file libStatic/globals.h:

extern int globvar;

Code file libStatic/globals.cpp:

int globvar = 42;

The DLL libDynamic and the executable runner are using this global variable. Furtheron, libDynamic is linked at run-time into runner (via LoadLibrary(), GetProcAddress(), and the works...)

I understand this will lead to globvar being created twice, once in the heap of runner and once in the heap of libDynamic, which is of course very undesirable.

Is there a good away around this? How can I ensure that libDynamic and runner are using the same globvar?

Answer 1

An easy way would be to let the .DLL point to the global variable of the executable. Right after loading you would call a special function inside that library (something like SetGlobVar(int*)). That way the library will always point to the same global variable as the .EXE.