collect2: error:ld returned 1 exit status solution

Collect2 :error: LD returned 1 exit status
This error occurred many times and has been solved before, but this time the same error occurred again, however, I have forgotten what caused it before, So, anyway, I have to write it down this time.
Given my experience with reporting so many errors, all of my reasons are: the same function name is used in both CPP files, even though they are in their own classes, but it doesn’t work, just change one of the function names to be OK.

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