Automatic record length determination

The routine RZOPEN can automatically determine the record length of existing RZ files. This is triggered by specifying a value of zero for the parameter LRECL on input. The record length is determined as follows:

• IBM systems (Fortran I/O only). The file is first opened for sequential access and a Fortran unformatted read is issued, using the IBM extension NUM=nbytes, e.g.

              READ(UNIT=LUNIT,NUM=LRECL) ITEST
  

  The file is then closed and reopened for direct-access I/O.
• VAX/VMS and Apollo systems (SR9) (Fortran I/O only). The file is first opened for sequential access and a Fortran inquire statment is issued, e.g.

              INQUIRE(UNIT=LUNIT,RECL=LRECL)
  

  The file is then closed and reopened for direct-access I/O.
• All other systems plus VAX/VMS systems using C I/O. The record length is determined from the data in the file itself. For this reason, the RZ package must know if the file is in native or exchange format. For this reason, the option 'X' is recommended when processing exchange format files.