Does Sinclair Spectrum BASIC have a maximum length for one line?

Question

I was just writing some junk Speccy Basic programs, more to see how they take up space on the +3's disk layout than to do any actual programming.

But I noticed that after editing a program line to make a very long REM statement, that most of what I added disappeared after I hit enter and in the listing instead of what I was typing I see some corrupted text instead REM QTQ NEXT PRINT at the end. Most of the program is REM statements so that one could be from memory stomping with part of the next line. Or not, since the rest is garbage.

Now I know that in the binary format of Spectrum BASIC there is a two byte field to hold the length in bytes for each line after tokenization.

But maybe some other part of the system has a much shorter limit, or maybe it's just a bug?

Is there a known limit, either by design or by accident?

Answer 1

The correct answer to your question is YES, and NO.

YES, if you are editing a long line in the editor of 128K BASIC, you are limited to the size of line buffer, which can hold only 20 screen rows. You can confirm this by reading the ZX ROM Disassembly which can be found here (note that you will need to be reading disassembly for ROM 0). Let me quote a comment from there, given under the heading "128 BASIC Mode Limitations":

There is a practical limitation on the size of lines that can be entered. It is limited to 20 indented rows, which is the size of the editing buffers. Typed lines greater than 20 rows get inserted into the BASIC program, but only the first 20 rows are shown on screen. Editing such a line causes it to be truncated to 20 rows. There is no warning when the 20 row limit is exceeded.

Just to illustrate this point, I quickly did the following steps:

1. I created a line that contains 21 rows:
2. I tried to press the return key, to see what gets saved (and frankly it looks fine at this stage!):
3. I tried to edit the line again, and then it becomes clear that things are not all rosy:
4. To make things properly interesting, I tried adding a space after the fullstop, just before the first word TEST at the end and pressed the return key to obtain

So, 128K BASIC editor is basically inadequate.

NO is also a correct answer, because the actual storage format of ZX BASIC allows lines with lengths up to almost 64K, which in any case cannot be inputted directly from BASIC. I believe that 48K BASIC is free from the described limitation and the line editor of 48K BASIC can only run into trouble saving your line if you run out of available RAM, which in 48K configuration can happen as your line length exceeds something like 20K of characters.

Answer 2

ZX Basic stores the length of each line as two-byte quantity, so the length of any line is limited only by the amount of available RAM.

In fact, it is a common thing to put binary executable code inside REM statement, where the whole basic looks like this:

10 RANDOMIZE USR addr:REM <binary code follows>

with addr pointing to the byte after REM token. Such trick allows one, for example, to put there a packed(!) title screen for a long-loading game, without ugly and lengthier process of loading unpacked data directly into the screen memory. Another option is to have there a custom loader.

From my practice, basic lines up to many tens of kilobytes are perfectly possible (but my experience is only with the binary code in REMs).