Adobe Animate, C extensibility, sample code `computeSum` undefined

Sorry to bother.

I'm working on a c extension and following the code example successfully compiled it into a dll. Here is my code.

Place the extension into the specified folder.

The defined DeviceInfo can be accessed normally, but the functions inside cannot be accessed. I'm not very familiar with C language. Please help me how to access the functions inside. There are really very few official examples.