80-Bus News

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To Read and then Write a Random file the steps are as follows :

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OPEN the file

Declare the Fields

GET the required Record from Disk, if records already exist, or INPUT the necessary data and build the record.

Process the Fields

PUT the record onto Disk.

Repeat 3 to 6 until all done

CLOSE the File

90 INPUT “Enter CALL to be found. “;CSGNS

100 110 120 150 140 150 160 170 180

‘do some input error checking here. OPEN “R",£1, “RADIOLOG. DAT”, 70 FIELD£1,18 AS NAMES,8 AS CALL$,20 AS TOWNS,16 AS COUNTY$,8 AS DATES

FOR RNUM=X TO Y “X,Y define range of record numbers to be read. GET£1 , RNUM

IF CALL$=CSGN$ THEN GOTO xxxx

NEXT RNUM

PRINT “Record not found. “

CLOSE£1

Line 110 – OPEN’s the file, declares it as RANDOM, and describes it as File

£1 until it is closed. The name of the Data file to be known as File £1 is RADIOLOG.DAT and it uses Records of 70 bytes.

Line 120 – Sets up the FIELDS for file £1. Each Field is given a Variable

‘Line 140

name and its length is set. GET’s each Record in turn from the Disk until the search either succeeds or fails altogether.

Line 150 – Looks for match between INPUT data and Disk record data. (N.B. in

this simplified example, Line 150 will probably fail to work since “430CB” does NOT equal “G30CB “. To work correctly, the trailing blanks would have to be removed, or the INPUT callsign padded out to 8 characters with blanks.

Line 160 – Continues looping until record found, or all done. Line 170 – Prints appropriate message. Line 180 – CLOSEs the file.

FIELDS

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Although it is possible to use the Data in the Fields directly, as in

line 150 above, it is normal practice to ‘move’ the Data out of the Field variable into some other variable for processing. There are several reasons for this:–

1) The Field data will contain leading or trailing blanks which can lead to

unreliable results when Processing or Printing Data.

2) Numeric data is stored in Fields as Strings. It must be converted back to numeric form for calculations.

3) Integers are stored as 2 Byte Fields, Single Precision as 4 Bytes, Double Precision as 8 Bytes.

4) It is often convenient to have the origional Field in uncorrupted form during processing.