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The second example (EX2.BAS) is a general purpose screen dump displaying
program, using a parameter file to control its action. Note how variables are INPUT
from the data file, with the EOF function allowing automatic variation in the size of
the file. It is important that the screen dump displayed by this program was saved with
the screen in a known position in memory, otherwise the result will be 'skewed'. This
is ensured by the saving program executing a MODE command and thereafter being
careful not to cause the screen to scroll.
10 DIM colour(15) : REM Provision for 16 colours
20 OPENIN “param.dat”
30 INPUT #9,filename$,screenmode
40 i=0
50 WHILE NOT EOF
60 INPUT #9, colour(i)
70 INK i, colour(i)
80 i=i+1
90 WEND
100 CLOSEIN
110 MODE screenmode:BORDER 0
120 LOAD filename$
2.4.2 Pre-empting a Garbage Collection.
If the program performing data file transactions has a number of string variables,
particularly string arrays, it will speed the OPENing of files if the computer is
persuaded not to perform a garbage collection at that time. Garbage collection is the
process by which the BASIC clears away and tidies up the memory space used for
strings in order to dynamically allocate a buffer for the file transfer.
If a program does indeed operate a number of string variables and arrays, incorporate
the lines below into the program, and a file buffer will be permanently allocated,
which will prevent garbage collection when subsequent files are opened. Note that the
lines below should be incorporated after any SYMBOL AFTER commands in the
program.
OPENOUT "DUMMY"
MEMORY HIMEM-1
CLOSEOUT
2.5 Reference guide to AMSDOS commands.
Refer to Chapter 8 in your CPC464 User Instruction manual if you are in any doubt
about the notation used, or the effect of particular commands when used with cassette.
AMSTRAD Disc Drive & Interface DDI-1 Manual Chapter 2. 6