When and where is the default workspace size determined? in C/C++ source code

I’m learning about blender’s interface on this site.

I’m also studying blender’s source code.

When and where is the workspace (3D Viewport, Outliner, etc.) size determined? in main function.
Size means that in addition to width and height, it also includes position

Is it before WM_main function?

The default workspaces and their sizes are loaded from release/datafiles/startup.blend, they are not in the source code.

The source code for editing the associated data structures, and adjusting to different screen resolutions is in the screen_*.cc files source/blender/editors/screen.