Code before warnings are enabled at line 6, column 1.  See page 431 of PBP.  (Severity: 4)
Return value of "close" ignored at line 432, column 2.  Check the return value of "close" for success.  (Severity: 2)
Return value of "open" ignored at line 437, column 2.  Check the return value of "open" for success.  (Severity: 3)
Return value of "close" ignored at line 441, column 2.  Check the return value of "close" for success.  (Severity: 2)