Some classes are not exported from MFC extension DLL

[amitdedhia]

Hi

I am migrating a product code (originally written in VS2003) to VS2005.
The application is written in VC++ (using MFC) and has mix of managed
and unmanaged classes. It is a desktop based application which controls
an instrument (a device) and interacts with it.

I fixed all the compiler errors and ran the application. I got a
message that "The procedure entry point XXX could not be located in the
dynamic link library AAAA.dll.

Upon using Dependency Walker, I realised that there are at least 5
classes which are not exported from one of the DLLs. (Rest all DLLs are
good). However, inside the code, the classes exported well using
AFX_EXT_CLASS macro before the class name. There are two points to note
here.
1) When the same code was copied as is, compiled and ran on another PC
in a different country (on VS2005), it ran well.
2) The DLL in question here is the one which interacts with the actual
instrument (device) using some third party DLLs.

I am not getting into any good direction. Can anyone guess what may be
happenning? Since the application ran well on some other machine, I
feel the code is ok. It has something to do with some configuration
setting. Can anyone guess?

Thanks in advance.

Amit Dedhia

 

[Doug Harrison [MVP]]

Hi

I am migrating a product code (originally written in VS2003) to VS2005.
The application is written in VC++ (using MFC) and has mix of managed
and unmanaged classes. It is a desktop based application which controls
an instrument (a device) and interacts with it.

I fixed all the compiler errors and ran the application. I got a
message that "The procedure entry point XXX could not be located in the
dynamic link library AAAA.dll.

Upon using Dependency Walker, I realised that there are at least 5
classes which are not exported from one of the DLLs. (Rest all DLLs are
good). However, inside the code, the classes exported well using
AFX_EXT_CLASS macro before the class name.

If Dependency Walker reveals the classes weren't exported, how is it they
"exported well inside the code"?

There are two points to note
here.
1) When the same code was copied as is, compiled and ran on another PC
in a different country (on VS2005), it ran well.
2) The DLL in question here is the one which interacts with the actual
instrument (device) using some third party DLLs.

I am not getting into any good direction. Can anyone guess what may be
happenning? Since the application ran well on some other machine, I
feel the code is ok. It has something to do with some configuration
setting. Can anyone guess?

The AFX_EXT_CLASS macro should be avoided, because it cannot be used in
multiple DLL scenarios, where one extension DLL uses another. Try replacing
your AFX_EXT_CLASS usage as follows:

In some DLL header file, which the other DLL headers #include, write the
following, replacing "X" with the name of your DLL, making sure it has a
reasonable chance of being unique:

#ifdef COMPILING_X_DLL
#define X_EXPORT __declspec(dllexport)
#else
#define X_EXPORT __declspec(dllimport)
#endif

Then #define COMPILING_X_DLL only in that DLL's project. This method can be
used by multiple DLLs, a big advantage over AFX_EXT_CLASS, and since the
macro names are unique, they don't conflict. Then you can do things like:

X_EXPORT void f();

class X_EXPORT MyClass
{
...
};

Look in the project's preprocessor options, and you may find the AppWizard
has already defined a suitable COMPILING_X_DLL macro for you.