Output the DLL instead of .exe with cmake/mingw - c++

Question

I'm not very familiar with both cmake and mingw.
I have some source code that can be build with it (and the build process works fine with mingw32-make). The problem is, I would like to output the DLLs and not the .exe files.
I have some CMakeList file that I believe stores the configuration I have to change (that part should be responsible to produce the .exe files for .cpp files in Examples/ directory, taking some dependencies into account):
# C examples
if(PSMOVE_BUILD_EXAMPLES)
foreach(EXAMPLE example multiple dump_calibration battery_check)
add_executable(${EXAMPLE} examples/c/${EXAMPLE}.c)
target_link_libraries(${EXAMPLE} psmoveapi)
endforeach()
if(PSMOVE_BUILD_TRACKER AND PSMOVE_BUILD_TUIO_SERVER)
include_directories(${PSMOVEAPI_SOURCE_DIR}/external/TUIO_CPP/TUIO)
include_directories(${PSMOVEAPI_SOURCE_DIR}/external/TUIO_CPP/oscpack)
add_executable(tuio_server examples/c/tuio_server.cpp
external/TUIO_CPP/TUIO/TuioClient.cpp
...
external/TUIO_CPP/oscpack/ip/win32/NetworkingUtils.cpp
external/TUIO_CPP/oscpack/ip/win32/UdpSocket.cpp)
set_target_properties(tuio_server PROPERTIES
COMPILE_FLAGS -DOSC_HOST_LITTLE_ENDIAN)
target_link_libraries(tuio_server psmoveapi psmoveapi_tracker)
else()
# Disable the TUIO Server if we don't build the tracker
set(PSMOVE_BUILD_TUIO_SERVER OFF)
endif()
if(PSMOVE_BUILD_TRACKER)
foreach(EXAMPLE distance_calibration)
add_executable(${EXAMPLE} examples/c/${EXAMPLE}.c)
target_link_libraries(${EXAMPLE} psmoveapi psmoveapi_tracker)
endforeach()
endif()
endif()
I guess I should add -DBUILDING_EXAMPLE_DLL and -shared options somewhere. But where exactly? Or maybe I'm missing the point?

Answer 1

To make a dll you need add_library(mydlltarget SHARED mysourcefiles) instead of add_executable(myexetarget mysourcefiles)
Also to make a dll from code that was an executable you will at minimum have to modify your headers to export the classes/functions that you want exported. From the documentation for building a dll with mingw it appears that the process is similar to Visual Studio. Where you have a header define a macro that translates to __declspec(dllexport) when building the dll and __declspec(dllimport) when using the dll.
A sample of the export header looks like this:
#ifdef BUILDING_EXAMPLE_DLL
#define EXAMPLE_DLL __declspec(dllexport)
#else
#define EXAMPLE_DLL __declspec(dllimport)
#endif
Then the modification for your class is like this:
class EXAMPLE_DLL MyClass
{
public:
MyClass() {};
virtual ~MyClass() {};
void func(void);
};
Then you need to define BUILDING_EXAMPLE_DLL when building the dll. You can do that in CMake with an add_definitions(-DBUILDING_EXAMPLE_DLL)
Also CMake provides support for generating the export header with GENERATE_EXPORT_HEADER
Doc for GenerateExportHeader