In VS2010 which functions are exported into a DLL?

Question

I am building a DLL to wrap a C/C++ library to be called from matlab.

I am using the standard __declspec(dllexport) to export functions. Specifically, I have several .h files with code that essentially looks like:

#ifdef __cplusplus 
extern "C" {
#endif

#ifdef _MSC_VER
__declspec(dllexport)
#endif
void FOO();

#ifdef __cplusplus 
}
#endif

Then, I have a lib.h file, that just includes all these .h files.

#include "foo.h"
#include "bar.h"

My project configuration is such that it does build a DLL, but the mystery is that BAR() is in the DLL (as verified by dumpbin) but FOO is not.

Any ideas on how this could possibly be the case?

Answer 1

In the example above, the problem was due to the fact that BAR did not have a definition in the source tree of the project.

I'm relatively new to TFS and VS, so let me see if I can explain this in a way that makes sense.

The solution has multiple projects. One project is called MatlabDLL, the main project is called OurLibrary. The Matlab DLL is not importing all of Library, just wraps parts of it for inclusion into Matlab. In many cases, Matlab DLL can easily call directly to the C functions, in other cases, functions have to be rewritten to handle Matlab C/DLL calling semantics.

So, BAR had to have a Matlab specific C wrapper around it to enable it to be called from Matlab. The associated source file bar.cpp was in the MatlabDLL project. (Under the hood, BAR calls a number of functions whose source lives in the OurLibrary project, none of whose source files are in the MatlabDLL project.)

FOO had an implementation that did not require a C specific wrapper, so foo.cpp lived in the OurLibrary part of the source tree, and had no source files in the MatlabDLL project, although it's associated .h file was referenced by MatlabDLL.h.

In the end, VS2010 appears to only build the __declspec(dllexport)'d functions that have associated c files in the project. Adding foo.c to the project fixed the problem.