Pitfalls for breaking up a large file into one DLL? - c++

Question

I am not that experienced in creating DLL's in MSVC++ 2010, just may be a few times as part of the learning curve. At the moment I have a very large file with about 10 different classes in it. I have to breakdown the file into multiple files and move out related classes to the same file. So before proceeding wanted to know from experienced developers about my situation.
Something like the following
// Header
namespace collections
{
classA
classB
ClassC
ClassD : ClassA,ClassB
}
// CPP
namespace collections
{
classA
{
// Implementations
}
// Rest of the classes
}
After breaking down to separate files
// ClassA.h
namespace Collections
{
ClassA
}
// ClassB.h
namespace Collections
{
ClassB
}
// Implentations etc
My main concern is the usage of dllexport/dllimport storage class attributes
Since The file will be broken up I would have to use the following
#ifdef MAKEDLL
# define EXPORT __declspec(dllexport)
#else
# define EXPORT __declspec(dllimport)
#endif
against the classes to export/import them. But placing these line in each header file that will be create (with one namespace "Collections"), will this have any bad implications while compiling or code generation step? I was looking around on-line and found out that people most complain about linker errors/warnings where a particular member is redefined or is not found whilst creating DLL's. This must definitely be a solved issue just that I dont know which is the best and proper way of doing it.
I need to create just one DLL in the end. I dont need to create multiple DLL's.
Any guidance or help is much appreciated.
Thank you

Answer 1

There is no issue to have one common header file that defines the EXPORTS macro:
mydll.h
#ifdef MYDLL_EXPORTS
#define MYDLL_API __declspec(dllexport)
#else
#define MYDLL_API __declspec(dllimport)
#endif
And have this header file included in other header files:
ClassA.h
#include "mydll.h"
namespace Collections
{
class MYDLL_API ClassA {
// ...
}
}
ClassA.cpp
#include "ClassA.h"
// ...
ClassB.h
#include "mydll.h"
namespace Collections
{
class MYDLL_API ClassB {
// ...
}
}
... and so on. You can have all of them (header files and .cpp implementation files) in one DLL, having MYDLL_EXPORTS defined in your DLL project settings (it is automatically done by the VS2010 DLL wizard).
There is nothing weird here. You never redefine anything.
You just use the handy MYDLL_API to add a decorator to all your DLL API classes.