Tape File Representation

A Fortran data file is represented on tape by a sequence of data records followed by an endfile record. The data is grouped into blocks, with maximum block size determined when the file is opened. The records are represented in the same way as records in disk files: formatted records are followed by newlines; unformatted records are preceded and followed by character counts. In general, there is no relation between Fortran records and tape blocks; that is, records can span blocks, which can contain parts of several records.

The only exception is that Fortran does not write an unformatted record that spans blocks; thus, the size of the largest unformatted record is eight characters less than the block size.

The dd Conversion Utility

An end-of-file record in Fortran maps directly into a tape mark. In this respect, Fortran files are the same as tape system files. But since the representation of Fortran files on tape is the same as that used in the rest of UNIX, naive Fortran programs cannot read 80-column card images on tape. If you have an existing Fortran program and an existing data tape to read with it, translate the tape using the dd(1) utility, which adds newlines and strips trailing blanks.

Example: Convert a tape on mt0 and pipe that to the executable ftnprg:

demo% dd if=/dev/rmt0 ibs=20b cbs=80 conv=unblock | ftnprg 

The getc Library Routine

As an alternative to dd, you can call the getc(3F) library routine to read characters from the tape. You can then combine the characters into a character variable and use internal I/O to transfer formatted data. See also TOPEN(3F).