TOPS-20 PASCAL Language Manual - Bitsavers

PASCAL D~TA
TYPES
2.3.4 File Types
A file is a sequence of data components of the same type. The number
of components in a file is not fixed; a file can be of any length.
The file type definition specifies the type of the file components.
Fo rma t
TYPE identifier
FILE OF component type
where:
component type specifies the type of the components of the
file. The component type can be any scalar
or structured type except a file type or an
array or record type containing a file
element or field.
The arithmetic, relational, Boolean, and assignment operators do not
work on file variables or structures containing file components. For
example, you cannot assign one file variable to another file variable,
nor can you initialize a file variable.
Type compatibility for files applies only to file parameters. Two
file parameters are compatible if their components are compatible and
if both are packed or neither is packed. You can pass a file only as
a VAR parameter.
PASCAL automatically creates a buffer variable for each file variable
you declare. The type of the buffer variable is the same as the type
of the file components. To denote the buffer variable, specify the
name of the associated file variable fo] lowed by a circumflex (~), for
example:
TYPE Scores = FILE OF INTEGER;
VAR Math_Scores: Scores;
PASCAL creates ~ath Scores~ as an integer buffer variable associated
with the file Math Scores. The buffer variable takes on the value of
the file at the cur~ent file position. The predeclared input and
output procedures move the file position, thus changing the value of
the buffer variable.
Example I
VAF, T ruthva 1. s FIL.E OF' BOOLEAN;
This declaration specifies a file of Boolean values.
variable for this file is denoted by Truthva]s~.
Example 2
TYPE Names = PACKED ARRAY [1 •• 20] OF CHAR;
Data .... Fi Ie :::: FILE or Names;
VAH Accept .... L..ist" RejecL.List, Wait_List: Data_File;
The
buffer
This example defines the array type Names and the file type DataFile,
which contains a list of names. The VAR section specifies three file
variables of type DataFile, with associated buffer variables
Accept_List~, Reject_List~, and Wait List~.
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