Code
substr("test")
Condition
Error in `substr()`:
! `start` must be a whole number, not absent.
Code
substr("test", 0)
Condition
Error in `substr()`:
! `stop` must be a whole number, not absent.
Code
substr("test", "x", 1)
Condition
Error in `substr()`:
! `start` must be a whole number, not the string "x".
Code
substr("test", 1, "x")
Condition
Error in `substr()`:
! `stop` must be a whole number, not the string "x".
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