Yes, you can do that.  You want to declare the functions (no classes!), as
extern "C", when the client of the DLL sees their declarations, so you need
to make sure to form the declarations correctly.  Something like this:

headerfile.h:

#ifdef __cplusplus
extern "C"
{
#endif

#ifdef BUILDING_THE_DLL_ITSELF
#define    EXPORTMODIFICATION    declspec(dllexport)
#else
#define    EXPORTMODIFICATION    declspec(dllimport)
#endif

EXPORTMODIFICATION int Function1(...);

EXPORTMODIFICATION int Function2(...);

#ifdef __cplusplus
}
#endif

This will pretty-much assure that you don't do anything 'bad', like try to
have two versions of the same function name with different parameters
(overloading the name), which is a C++-only capability.  The
EXPORTMODIFICATION symbol helps to assure that, when you're actually
building the DLL, as opposed to some other module that just uses it, that
you're getting the right modifiers on the function to make it exported from
the DLL.  When a client of the EXE is being built, you get a suitable
'external' reference to the function which should be resolved when you link
the EXE by linking with the import library for the DLL.  It's easier to see,
when you do it, than it is to explain clearly in a newsgroup post
(obviously!)...

Paul T.