String heap management

[Hated Moron]

The help claims that DIM p% -1 is the equivalent of PRINT HIMEM-END

I hope it doesn't! The statements which are (precisely) equivalent are:

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      DIM p% -1  : REM Set p% to end of heap
      p% = END   : REM Set p% to end of heap

Although of course the returned value is not guaranteed to fit in a 32-bit integer on a 64-bit system, so this should really be:

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      DIM p%% -1 : REM Set p%% to end of heap
      p%% = END  : REM Set p%% to end of heap

but I don't think that can be true, because the DIM statement actually reserves some memory.

Note the statement, "The amount of memory reserved is one byte greater than the value specified. DIM p%% −1 is a special case; it reserves zero bytes of memory." In other words, it reserves -1 bytes +1 byte, which is indeed zero but I suspect that some zeros are worth more than others.

I don't know what you mean by "some zeros are worth more than others". It's easy to see how much memory is 'reserved' by repeating the operation:

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      DIM p%% -1 : PRINT END
      DIM p%% -1 : PRINT END
      DIM p%% -1 : PRINT END
      DIM p%% -1 : PRINT END
      DIM p%% -1 : PRINT END

You should find that the same value is printed each time, confirming that no heap memory is allocated.

Surely if all you want to do is remove trailing spaces, something like this would solve your problem?

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DEFFNtrim(a$):LOCALl%
l%=LENa$
REPEAT:l%-=1:UNTILMID$(a$,l%,1)>" "
=LEFT$(a$,l%)

The easiest (but not necessarily the fastest) way to remove trailing spaces in BBC BASIC is as follows:

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      WHILE RIGHT$(a$) = " " : a$ = LEFT$(a$) : ENDWHILE