C-DLL from C++ source
Question
I have a C-Wrapper for my C++ Framework. Since this should run on mac and windows I am using scons:
env = Environment()
env.Append(CPPPATH = ['./'])
env.Append(LIBS = 'kernel32.lib')
env.Append(LIBPATH = 'C:/Program Files/Microsoft SDKs/Windows/v6.0A/Lib')
env.SharedLibrary(target='warpLib', source='warplib.cpp')
Simple Versions of warplib.cpp and warplib.h look like this:
warplib.cpp
#define DllExport __declspec( dllexport )
#include "warplib.h"
extern "C" {
DllExport int foo(int a) {
return a;
}
}
warplib.h
#define DllExport __declspec( dllexport )
extern "C" {
DllExport int foo(int a);
}
Can anybody tell me what is wrong with that? I tried almost all the combinations possible of 'extern "C"' but it always throws me something like "error C2732: linkage specification contradicts earlier specification for '...'".
If I skip 'extern "C"' it works but I see no .lib file and I am pretty sure I need that to really use the library.
Solution
You should only need extern "C"
on the declaration. Anyone then including that header will expect to link against it using the C linking standard, rather than the C++ decorated form. The warplib.cpp
source file, and subsequent object file will expose the function foo
correctly if warplib.h
is included.
When using MSVC, there are a plethora of semi-useful scripts, and "build environment" console shortcuts provided, with a lot of dev-related environment variables and paths provided. I recommend locating a suitable script to execute to insert these variables into your environment, or running the dev console.