Question:
I have a C++ project with the following definition in the header file:
typedef enum /* Set operation type */ { GPC_DIFF, /* Difference */ GPC_INT, /* Intersection */ GPC_XOR, /* Exclusive or */ GPC_UNION /* Union */ } gpc_op; typedef struct /* Polygon vertex structure */ { double x; /* Vertex x component */ double y; /* vertex y component */ } gpc_vertex; typedef struct /* Vertex list structure */ { int num_vertices; /* Number of vertices in list */ gpc_vertex *vertex; /* Vertex array pointer */ } gpc_vertex_list; typedef struct /* Polygon set structure */ { int num_contours; /* Number of contours in polygon */ int *hole; /* Hole / external contour flags */ gpc_vertex_list *contour; /* Contour array pointer */ } gpc_polygon; void gpc_polygon_clip (gpc_op set_operation, gpc_polygon *subject_polygon, gpc_polygon *clip_polygon, gpc_polygon *result_polygon); And I compile it in VS 2008. It can compile! So far so good.
Next I want to call the C++ dll from .Net, and I do a standard PInvoke:
[DllImport("gpc.dll")] private static extern void gpc_polygon_clip([In] GpcOperation set_operation, [In] ref gpc_polygon subject_polygon, [In] ref gpc_polygon clip_polygon, [In, Out] ref gpc_polygon result_polygon); But when I run the code, I get an "unable to find an entry point name * in DLL 'gpc.dll'".
I think my C++ vcproj setting must be wrong, because it seems that the definition is not exported. Any idea how to fix this?
Solution:1
extern "C" __declspec(dllexport) void gpc_polygon_clip (gpc_opset_operation, gpc_polygon *subject_polygon, gpc_polygon *clip_polygon, gpc_polygon *result_polygon); try out above in c++ vc project.
Solution:2
gpc_polygon_clip is not marked for export. It should use __declspec( dllexport ). Have a look here.
Solution:3
There are a number of ways. Probably the easiest is to prefix __declspec(dllexport) / __declspec(dllimport) to the declaration (when compiling the DLL or using it, respectively)
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