"error: unknown type name" in

ROOT
6

Is that code actually executed when loading the library?

Yes.

The line of gInterpreter->Declare("#include \"AOpticsManager.h\""); is executed right after the library is manually or automatically loaded because of the GCC or Clang’s functionality of __attribute__((constructor)).

Is the library loaded before loading the script?

No.

When I do not load my library before loading or executing my script, as you know, the library loading process is of course automatically done.

I tried three different cases.

  1. NG
root [0] .x test.C
root [1] #include "AOpticsManager.h"
root [2] .x test.C
  1. OK
root [0] #include "AOpticsManager.h"
root [1] .x test.C
root [2] .x test.C
  1. OK
root [0] gSystem->Load("libROBAST")
root [1] .x test.C
root [2] .x test.C

From your explanation in the threads, I understand why cases 2 and 3 work because the root [0] line in both cases loads the library first. But I do not understand why the 1st case does NOT work, while inserting #include in the script resolves the issue.