Global and static variables in a DLL module are, by default, not shared between processes which load the DLL, as a result, each process has its own instance of a DLL’s global and static variables.
To share DLL global and static variables amongst all processes which load the DLL, you must place the shared variables in a new data segment;
int nSomeSharedVariable = 0; // initialise variable
You then need to tell the linker about this data segment and mark it “shared”.
#pragma comment(linker, "/SECTION:.DATASEGNAME,RWS")
Having done this, variable nSomeSharedVariable is shared between all processes which load the DLL. This obviously means that you must protect such variables from access by multiple threads.