Re: how to export global variable in C dll?

From:

"Alex Blekhman" <tkfx.REMOVE@yahoo.com>

Newsgroups:

microsoft.public.vc.language

Date:

Thu, 10 Apr 2008 11:50:50 +0300

Message-ID:

<uf2v7fumIHA.3940@TK2MSFTNGP05.phx.gbl>

"Cyrfer" wrote:

I've found a fix for my problem, but I'm still looking for
documentation on declaring global variables for C (and C++ now
too)
DLLs.

It appears that one should export global variables in C DLLs the
same
way as one does in C++ DLLs, prefixing the global declarations
with
'__declspec( exp/imp )'.

With respect to export/import it doesn't mater whether the DLL is
C++ or C. `__declspec( export/import )' just marks the name to be
exported/imported.

You can export global variable in the same manner as you export a
function:

DLL.h file:

extern MYDLLEXP int g_data;

DLL.cpp (or DLL.c) file:

MYDLLEXP int g_data = 0;

Where `MYDLLEXP' macro expands to "__declspec( export/import )"
depends on project settings.

KB90530 - "HOWTO: How To Export Data from a DLL or an Application"
http://support.microsoft.com/kb/90530

In my case, I see linking errors when doing it because I had a
file
in my C DLL project that ended with the .cpp file extension.
Even
though all types were C, the C++ compiler must have been used to
compile my DLL. I don't know why I see a link error when using
the
export prefix, but changing my .cpp to have the .c file
extension
fixed the problem.

It happens because C++ compiler "mangles" exported names. Google
for "name mangling" for further info. If you want to control
exported names you can use .DEF file. Here's more info:

"Importing and Exporting"
http://msdn2.microsoft.com/en-us/library/9h658af8.aspx

HTH
Alex