80-Bus News

  

July-August 1984, Volume 3, Issue 4











Page 37 of 43











37

Now onto XBASIC. For sixty odd quid you get a disk with the ordinary interpreter plus the GXBASIC, the graphics version for the AVC. With AVCTXT sitting at the top of ram to give the 80 column screen (55K System size), the former gives you 35122 bytes of ram, the latter only 27105 bytes ! I won’t retramp the areas covered by Roger Dowling, just get straight into the disk handling stuff. Well, it’s really a bit of a mess, but somehow Lucas Logic came out with some twists to almost make up for it. I think they’ve gone down the road of – wait for it – BBC BASIC (sorry, quick, drink a glass of water, or something a bit stonger). I’ve used MBASIC on a Superbrain and it was quite nice. XBASIC lost me three days figuring out how to use the random access files without screwing up. The relevant commands are –

DRIVE <letter> – selects which drive to be logged in, -A’ is drive 0.

CREATE <F>,<SV>,<I> – creates a file with name “F’, -SV’ sets up buffer space and system variables, -I determines how long the random record length is. The range of -I’ is 0-65535. If -I” is not specified or 0, then the file is deemed for sequential access only. Any existing file with the same name is first deleted and an empty one then created.

OPEN <F>,<SV>,<I> – this is the same as for CREATE, If the file doesn’t exist then you get a -No File error’.

CLOSE <SVl..n> – closes the named files. CLOSE alone will close ALL open files.

APPEND <F>,<SV> – this is useful for sticking data onto the end of sequential files without having to read to the end first, so saving a lot of time. It doesn’t work with random files as you can specify which record you want to go to any way.

Now comes the daft bit, or B**b method. To get data in and out of files you have to direct the computer with the following –

PRINT £ <SV>,<I>;<variable(s)> – the variable(s) are output to the opened file with system variable name -SV*. ANY output from now on until otherwise redefined will go to that file. So if you forget the drive purrs away quite oblivious to the fact that it’s just ruined an evenings work.

INPUT £ <SV>,<I>;<variable(s)> – this is the opposite of PRINT £ (why they couldn’t have used DISCIN and DISCOUT or similar is beyond my logical brain). Like PRINT £ if you forget to redefine the input you get one hell of a mess. To redefine you can CLOSE <SV>, or do another PRINT £ <SV>,<I> (or INPUT £ <SV>,<I>) or PRINT £0 (or INPUT £0) so that the file(s) remain open. To backtrack a bit, the “SV” has to be a string variable and Lucas Logic claim it to be a wonderful idea as you can have lots of files open at the same time and because it’s a string variable, when not in use the memory is a available for use by something else. Sounds good doesn’t it ? So, what took me three days to work out ? Well, for one thing I had to learn to redefine the output and input. Secondly, when using random files the record length is not what you tell the computer. The manual doesn’t make it clear that the end of record marker (two bytes) is INCLUDED in the record length. So if you specify a record length of 50 bytes and output 50 bytes, two bytes are stuck on the end. When you then input the file you run out of string space as the whole file is dragged


This is an OCR’d version of the scanned page and likely contains recognition errors.











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