Trying to make a unity plugin for android with Visual Studio/C++: iostream not found

Hey all. After much googling, I landed here as no similar problems I read about were my exact cocktail of issues. Here’s what I’ve done so far:

-successfully put out a very simple, one function dll plugin for unity using Visual Studio/C++ that works. I used the Windows openCV package with openworld_341.dll.

-tried producing an android plugin from the same solution. I tried to do this by switching from x64 to ARM and from dll to static library, then had it export as .a instead of .lib…which builds successfully, but Unity refuses to recognize the .a file while running on android. Maybe I’m naive in thinking that was all I had to do?

-tried restarting a new project in Visual C++ with Android, C++ and a shared library as a target, using folders from the actual Android sdk of OpenCV (thinking maybe I was an idiot for not doing this first). Now it lets me build to .so, which is great. I added in the usual library folders and proper dependencies.
However – my last issue seems to be that for whatever reason, this Visual C++ Android dynamic shared library solution does not have iostream.h or stdio.h. What am I missing here, other than the obvious? When I built a project for windows/x64, these were findable automatically.