BBC BASIC Programmers' Reference

by Jon Ripley, May 2011

It is useful sometimes to be able to list the contents of a block of memory to examine it. This may be to help debug a problem, examine binary data in memory or one of many other uses.

The easiest way to achieve that is probably to use the supplied Memory Monitor add-in utility, which optionally displays the contents of a block of memory in hexadecimal and ANSI (commonly known as a hex dump).

However if you want to achieve a similar effect in your own program you can use PROCm_Dump below; it accepts four parameters:

      PROCm_dump(block%, size%, items%, verbose%)

Here block% should point to the memory to list, size% is the size in bytes, items% is the number of bytes to display on each line – typically 16 – and verbose controls whether a header is printed.

In the example below we reserve 16 bytes of memory, write a message into the memory and call PROCm_dump to display a hex dump of the memory:

      DIM a 15
      $$a="Hello world!"
      PROCm_dump(a, 16, 8, TRUE)

The ouput of the code is as follows:

Address  : 00 01 02 03 04 05 06 07 :

04421AA1 : 48 65 6C 6C 6F 20 77 6F : Hello wo
04421AA9 : 72 6C 64 21 00 00 00 00 : rld!....

Here is the code for PROCm_dump:

      DEF PROCm_dump(P%,L%,S%,F%)
      LOCAL I%,J%,K%
      FOR I%=0 TO L%-1 STEP S%
        IF I%MOD(S%*16)=0 IF F% THEN
          PRINT '"Address  :";
          FOR J%=0 TO S%-1
            PRINT " ";FNh0(J%,2);
          NEXT J%
          PRINT " :"'
        ENDIF
        PRINT FNh0(P%+I%,8)" :";
        FOR J%=0 TO S%-1
          K%=?(P%+I%+J%)
          IF P%+I%+J%<P%+L% THEN
            PRINT " ";FNh0(K%,2);
          ELSE
            PRINT "   ";
          ENDIF
        NEXT J%
        PRINT " : ";
        FOR J%=0 TO S%-1
          K%=?(P%+I%+J%)
          IF K%<32 OR K%>126 K%=ASC"."
          IF P%+I%+J%>=P%+L% K%=ASC" "
          VDU K%
        NEXT J%
        PRINT
      NEXT I%
      ENDPROC

      DEF FNh0(N%,L%)
      =RIGHT$(STRING$(L%,"0")+STR$~N%,L%)