Records and Files

A record is a sequence of characters and values; a sequence of records form a file. You can think of a file as a typed page, with the records being the lines of text.

A file can have sequential access (records are read one after the other) or random access (any record, specified by its number, can be accessed any time). The last record in a file is of special type, called the endfile record (it allows the automatic detection of the end of the file during reading).

In this part we talk about external files, stored on external medium - like the hard disk.

A program can read or write formatted or unformatted records.

Formatted records

• are composed of ASCII characters only
• information is in human-readable form
• when writing a formatted record, numbers are converted from internal, binary representation, to decimal, according to the edit descriptor specification. This conversion introduces roundoff, computational overhead, and results in a larger file.
• formatted data files are portable.

The following statement writes one formatted record; the format is explicitly given (F7.3)

write (unit=10, fmt="f7.3") r1

Unformatted records

• store data in the binary form, as represented internally by the computer.
• information is not human-readable
• there is no roundoff, no computational overhead, and results in a smaller file.
• unformatted data files may not be portable, since the internal representation may be different on different computer systems; however, they are useful to temporarily store intermediate results during one execution.

The following statement writes one unformatted record; no format is given

write (unit=10) r1

Unformatted data can be retrieved by unformatted read; the following statement reads one record; again, no format is specified.

read (unit=10) x1

Note that unformatted files may not be portable from one system to another.