Amos Professional Manual Contents Index

Disc Access

Random access files
AMOS Professional takes full advantage of the second type of file used by the Amiga. Random access files are extremely useful, because they allow the programmer to access data stored on a disc in any random order. A random access file is made up of units of data called "records", and each record has its own identification number. Every record can be split up into as many smaller sections as required, with every section becoming a "field". Each field is used to hold a single item of data.

The main difference between sequential files and random access files is that you must tell AMOS Professional the maximum size of a field in advance, before you can make use of it.

A field can hold many forms of data, like a password, an invoice number or even a literary quotation. Supposing you want to create an electronic phone book. You could choose the following fields, with the following maximum number of characters in each:

Field               Max. length
SURNAME$            20
F1RSTNAME$          15
TEL$                10

Once the fields have been planned, the structure for your electronic database can be set up using the following commands.

OPEN RANDOM
instruction: open a channel to a random access file
Open Random channel,filename$

This command is used to open a channel to a random access file, like this:

X> Open Random 1,"ADDRESS"

FIELD instruction: define a record structure
Field channel,length1 As field1$,length2 As field2$

FIELD$ should be used immediately after OPEN RANDOM to define a record that will be used for a random access file. This record can be up to 65535 bytes long. After selecting the channel number, give the maximum number of characters you will cater for in a field, followed by its name, then repeat the process as necessary. For example:

X> Field 1,20 As SURNAME$,15 As F1RSTNAME$,10 As TEL$

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10.02.14