解决方法
用于声明导入函数的c#语法在c中不可用.这里有一些关于如何使用DLL的其他SO问题：
> Explicit Loading of DLL
> Compile a DLL in C/C++,then call it from another program
> Calling functions in a DLL from C++
> Call function in c++ dll without header
> How to use dll’s?
> Is this a good way to use dlls? (C++?)
