从另一个dll调用函数时，DLL变得无法加载

Question

Now I have a Unity (C#) project, which calls my C++ project from a dll. They both worked fine, so as calling C++ functions from Unity.

However, when I try add one line to call a function another library (NLOpt library, from another dll) in the C++ project, the generated dll becomes unable to be loaded in the Unity project.

Plugin.h

extern "C" __declspec(dllexport) bool __stdcall LoadData(int agent_num, int frame_num, float* data);

Plugin.cpp

#include "Plugin.h"
#include <nlopt.h>
__declspec(dllexport) bool __stdcall LoadData(int agent_num, int frame_num, float* d)
{
    ...
    nlopt_opt opt = nlopt_create(NLOPT_LN_COBYLA, 3); //this line
}

As I add the line above, Unity will the following error:

Plugins: Failed to load 'Assets/Plugins/BirdOpti/BirdOpti.dll'

and

DllNotFoundException: Opti

I have tried couple of times so I am sure the problem is the line.

Did I do anything wrong?

Answer 1

将使用过的dll文件也添加到插件目录即可解决该问题。