I'd like a simple example of exporting a function from a C++ Windows DLL.
I'd like to see the header, the .cpp
file, and the .def
file (if absolutely required).
I'd like the exported name to be undecorated. I'd like to use the most standard calling convention (__stdcall
?). I'd like the use __declspec(dllexport)
and not have to use a .def
file.
For example:
//header
extern "C"
{
__declspec(dllexport) int __stdcall foo(long bar);
}
//cpp
int __stdcall foo(long bar)
{
return 0;
}
I'm trying to avoid the linker added underscores and/or numbers (byte counts?) to the name.
I'm OK with not supporting dllimport
and dllexport
using the same header. I don't want any information about exporting C++ class methods, just c-style global functions.
UPDATE
Not including the calling convention (and using extern "C"
) gives me the export names as I like, but what does that mean? Is whatever default calling convention I'm getting what pinvoke (.NET), declare (vb6), and GetProcAddress
would expect? (I guess for GetProcAddress
it would depend on the function pointer the caller created).
I want this DLL to be used without a header file, so I don't really need the a lot of the fancy #defines
to make the header usable by a caller.
I'm OK with an answer being that I have to use a *.def
file.
If you want plain C exports, use a C project not C++. C++ DLLs rely on name-mangling for all the C++isms (namespaces etc...). You can compile your code as C by going into your project settings under C/C++->Advanced, there is an option "Compile As" which corresponds to the compiler switches /TP and /TC.
If you still want to use C++ to write the internals of your lib but export some functions unmangled for use outside C++, see the second section below.
Exporting/Importing DLL Libs in VC++
What you really want to do is define a conditional macro in a header that will be included in all of the source files in your DLL project:
Then on a function that you want to be exported you use
LIBRARY_API
:In your library build project create a define
LIBRARY_EXPORTS
this will cause your functions to be exported for your DLL build.Since
LIBRARY_EXPORTS
will not be defined in a project consuming the DLL, when that project includes the header file of your library all of the functions will be imported instead.If your library is to be cross-platform you can define LIBRARY_API as nothing when not on Windows:
When using dllexport/dllimport you do not need to use DEF files, if you use DEF files you do not need to use dllexport/dllimport. The two methods accomplish the same task different ways, I believe that dllexport/dllimport is the recommended method out of the two.
Exporting unmangled functions from a C++ DLL for LoadLibrary/PInvoke
If you need this to use LoadLibrary and GetProcAddress, or maybe importing from another language (i.e PInvoke from .NET, or FFI in Python/R etc) you can use
extern "C"
inline with your dllexport to tell the C++ compiler not to mangle the names. And since we are using GetProcAddress instead of dllimport we don't need to do the ifdef dance from above, just a simple dllexport:The Code:
And here's what the exports look like with Dumpbin /exports:
So this code works fine: