Open Watcom FORTRAN 77 Language Reference

Language Reference
10.3 Records
FORTRAN distinguishes between three kinds of records, namely:
1. Formatted
2. Unformatted
3. Endfile
We shall describe each of these in the following sections.
10.3.1 Formatted Record
A formatted record consists of characters. The length of a formatted record is determined by the number of
characters in it. A formatted record may contain no characters at all and thus has zero length. Formatted
records are read or written using formatted input/output statements. An excellent example of a file
consisting of formatted records is our telephone book example.
10.3.2 Unformatted Record
An unformatted record consists of values such as integers, real numbers, complex numbers, etc. It may also
consist of characters. Essentially, these values have the same representation in a record as they have in the
computer’s memory. The length of an unformatted record depends on the amount of storage required to
represent these values in the computer’s memory. For example, on this computer an integer value is stored
using 4 bytes of memory (a byte is a grouping of 8 binary digits). Thus, integer values in unformatted
records also require 4 bytes of storage. For example, 3 integer values stored in an unformatted record
would require 12 bytes of storage. Unformatted records are read or written using unformatted input/output
statements.
To illustrate the difference between a formatted and unformatted record consider the following example.
Example:
INTEGER NUMBER
NUMBER=12345
PRINT 100, NUMBER
100 FORMAT(1X,I5)
WRITE( UNIT=7 ) NUMBER
If you print the variable NUMBER on a printer, it requires 5 character positions. If you write it to a file
using an unformatted WRITE statement, it only requires 4 bytes or character positions in the record. Note
that a character is conveniently represented in one byte of storage, hence we sometimes use the term "byte"
or "character" interchangeably when talking about the size of variables.
10.3.3 Endfile Record
An endfile record is a special record that follows all other records in a file. Simply stated, an endfile record
occurs at the end of a file. Actually, an endfile record is a conceptual thing. It has no length. When the
end of a file is reached (i.e., an attempt to read a record results in the endfile record being read), an
"end-of-file" condition exists. There are no more records following the endfile record. There is only one
endfile record so it is strictly illegal to attempt to read another record after the endfile record has been read
(i.e., when the end-of-file condition exists).
216 Records