R. T. RUSSELL

BBC BASIC (Z80) Manual

The section on serial files is split into three parts. The first deals with character data files. These are the simplest type of files to use and the examples are correspondingly short. The second part looks at mixed numeric/character data files. The final part describes conversion between BBC BASIC (Z80) format files and the file formats required/produced by other systems.

Character Data Files

The first three examples are programs to write data in character format to a serial file and to read the data back. All the data is in character format and, since the files will not be read by other versions of BASIC, no extra control characters have been added.

You may notice that we have cheated a little in that a procedure is called to close the files and end the program without returning. This saves using a GOTO, but leaves the return address on the stack. However, ending a program clears the stack and no harm is done. You should not use this sort of trick anywhere else in a program. If you do you will quickly use up memory.

Ex 1 - Writing Serial Character Data

 10 REM F-WSER1
 20 :
 30 REM WRITING TO A SERIAL CHARACTER DATA FILE
 40 :
 50 REM This program opens a data file and writes
 60 REM serial character data to it.  The use of
 70 REM OPENOUT ensures that, even if the file
 80 REM existed before, it is cleared before 
 90 REM being written to.
100 :
110 phonenos=OPENOUT "PHONENOS"
120 PRINT "File Name PHONENOS Opened as Handle ";phonenos
130 PRINT
140 REPEAT
150   INPUT "Name ? " name$
160   IF name$="" THEN PROC_end
170   INPUT "Phone Number ? " phone$
180   PRINT
190   PRINT#phonenos,name$,phone$
200 UNTIL FALSE
210 :
220 DEF PROC_end
230 CLOSE#phonenos
240 END

Ex 2 - Reading Serial Character Data

 10 REM F-RSER1
 20 :
 30 REM EXAMPLE OF READING A SERIAL CHARACTER FILE
 40 :
 50 REM This program opens a previously written
 60 REM serial file and reads it.
 70 :
 80 :
 90 phonenos=OPENIN "PHONENOS"
100 PRINT "File Name PHONENOS Opened as Handle ";phonenos
110 PRINT
120 REPEAT
130   INPUT#phonenos,name$,phone$
140   PRINT name$,phone$
150 UNTIL EOF#phonenos
160 :
170 CLOSE#phonenos
180 END

Ex 3 - Writing 'AT END' of Character Files

The next example extends the write program from Example 1. This new program opens the file, sets PTR# to the end (line 380) and then adds data to it. A procedure is used to open the file. This has the advantage of making the program more understandable by putting the detailed 'open at end' coding out of the main flow of the program.

 10 REM F-WESER1
 20 :
 30 REM EXAMPLE OF WRITING TO THE END OF A SERIAL DATA FILE
 40 :
 50 REM The program opens a file and sets PTR
 60 REM to the end before writing data to it.
 70 :
 80 REM A function is used to open the file.
 90 :
100 :
110 phonenos=FN_openend("PHONENOS")
120 PRINT "File Name PHONENOS Opened as Handle ";phonenos
130 PRINT
140 REPEAT
150   INPUT "Name ? " name$
160   IF name$="" THEN PROC_end
170   INPUT "Phone Number ? " phone$
180   PRINT
190   PRINT#phonenos,name$,phone$
200 UNTIL FALSE
210 :
220 DEF PROC_end
230 CLOSE#phonenos
240 END
250 :
260 :
270 REM Open the file 'AT END'.
280 :
290 REM If the file does not already exist, it
300 REM is created with OPENOUT.  PTR# is left
310 REM at zero and the handle is returned.  If
320 REM the file exists, PTR# is set to the end
330 REM and the file handle returned.
340 DEF FN_openend(name$)
350 LOCAL fnum
360 fnum=OPENUP(name$)
370 IF fnum=0 THEN fnum=OPENOUT(name$): =fnum
380 PTR#fnum=EXT#fnum
390 =fnum

Mixed Numeric/Character Data Files

The second three examples are also programs which write data to a file and read it back, but this time the data is mixed. They are simply extensions of the previous examples which illustrate the handling of mixed data.

Ex 4 - Writing a Mixed Data File

 10 REM F-WSER2
 20 :
 30 REM EXAMPLE OF WRITING TO A MIXED NUMERIC/CHAR DATA FILE
 40 :
 50 REM This program opens a file and writes
 60 REM numeric and char data to it.  The use
 70 REM of OPENOUT ensures that, even if the
 80 REM file exists, it is cleared before
 90 REM being written to.  Functions
100 REM are used to accept and validate
110 REM the data before writing it to the file.
120 :
130 :
140 stats=OPENOUT("STATS")
150 PRINT "File Name STATS Opened as Handle ";stats
160 PRINT
170 REPEAT
180   name$=FN_name
190   IF name$="" THEN PROC_end
200   age=FN_age
210   height=FN_height
220   sex$=FN_sex
230   PRINT
240   PRINT#stats,name$,age,height,sex$
250 UNTIL FALSE
260 :
270 DEF PROC_end
280 PRINT "The file is ";EXT#stats;" bytes long"
290 CLOSE#stats
300 END
310 :
320 :
330 REM Accept a name from the keyboard and make
340 REM sure it consists only of spaces and
350 REM upper or lower case characters. Leading
360 REM spaces are ignored on input.
370 :
380 DEF FN_name
390 LOCAL name$,FLAG,n
400 REPEAT
410   FLAG=TRUE
420   INPUT "Name ? " name$
430   IF name$="" THEN 490
440   FOR I=1 TO LEN(name$)
450     n=ASC(MID$(name$,I,1))
460     IF NOT(n=32 OR n>64 AND n<91 OR n>96 AND n<123) THEN FLAG=FALSE
470   NEXT
480   IF NOT FLAG THEN PRINT "No funny characters please !!!"
490 UNTIL FLAG
500 =name$
510 :
520 :
530 REM Accept the age from the keyboard and
540 REM round to one place of decimals.  Ages
550 REM of 0 or less, or 150 or more are
560 REM considere dto be in error.
570 DEF FN_age
580 LOCAL age
590 REPEAT
600   INPUT "What age ? " age
610   IF age<=0 OR age >=150 THEN PRINT "No impossible ages please !!!"
620 UNTIL age>0 AND age<150
630 =INT(age*10+.5)/10
640 :
650 :
660 REM Accept the height in centimetres from
670 REM the keyboard and round to an integer.
680 REM Heights of 50 or less and 230 or more
690 REM are considered to be in error.
700 DEF FN_height
710 LOCAL height
720 REPEAT
730   INPUT "Height in centimetres ? " height
740   IF height<=50 OR height>=230 THEN PRINT "Very funny !!!"
750 UNTIL height>50 AND height<230
760 =INT(height+.5)
770 :
780 :
790 REM Accept the sex from the keyboard.  Only
800 REM words beginning with upper or lower case
810 REM M or F are OK.  The returned string is
820 REM truncated to 1 character.
830 DEF FN_sex
840 LOCAL sex$,FLAG
850 REPEAT
860   FLAG=TRUE
870   INPUT "Male or Female - M or F ? " sex$
880   IF sex$<>"" THEN sex$=CHR$(ASC(MID$(sex$,1,1)) AND 95)
890   IF sex$<>"M" AND sex$<>"F" THEN FLAG=FALSE
900   IF NOT FLAG THEN PRINT "No more sex(es) please !!!"
910 UNTIL FLAG
920 =sex$

Ex 5 - Reading a Mixed Data File

 10 REM F-RSER2
 20 :
 30 REM EXAMPLE OF READING FROM A MIXED NUMERIC/CHAR DATA FILE
 40 :
 50 REM This program opens a file and reads
 60 REM numeric and character data from it.
 70 :
 80 :
 90 stats=OPENIN("STATS")
100 PRINT "File Name STATS Opened as Handle ";stats
110 PRINT
120 REPEAT
130   INPUT#stats,name$,age,height,sex$
140   PRINT "Name ";name$
150   PRINT "Age ";age
160   PRINT "Height in centimetres ";height
170   IF sex$="M" THEN PRINT "Male" ELSE PRINT "Female"
180   PRINT
190 UNTIL EOF#stats
200 :
210 CLOSE#stats
220 END

Ex 6 - Writing 'AT END' of Mixed Files

This example is similar to Example 3, but for a mixed data file.

  10 REM F-WESER2
  20 :
  30 REM EXAMPLE OF WRITING AT THE END OF A
  40 REM MIXED NUMERIC/CHAR DATA FILE
  50 :
  60 REM This program opens a file, sets PTR
  70 REM to its end and then writes numeric and
  80 REM character data to it.
  90 :
 100 REM Functions are used to accept and
 110 REM validate the data before writing it to
 120 REM the file.
 130 :
 140 stats=FN_open("STATS")
 150 PRINT "File Name STATS Opened as Handle ";stats
 160 PRINT
 170 REPEAT
 180   name$=FN_name
 190   IF name$="" THEN PROC_end
 200   age=FN_age
 210   height=FN_height
 220   sex$=FN_sex
 230   PRINT
 240   PRINT#stats,name$,age,height,sex$
 250 UNTIL FALSE
 260 :
 270 DEF PROC_end
 280 PRINT "The file is ";EXT#stats;" bytes long"
 290 CLOSE#stats
 300 END
 310 :
 320 :
 330 REM Open the file.  If it exists, set PTR#
 340 REM to vthe end and return the handle.  If
 350 REM it does not exist, open it, leave PTR#
 360 REM as it is and return the file handle.
 370 DEF FN_open(name$)
 380 LOCAL fnum
 390 fnum=OPENUP(name$)
 400 IF fnum=0 THEN fnum=OPENOUT(name$): =fnum
 410 PTR#fnum=EXT#fnum
 420 =fnum
 430 :
 440 :
 450 REM Accept a name from the keyboard and make
 460 REM sure it consists of spaces and upper or
 470 REM lower case characters.  Leading spaces
 480 REM are automatically ignored on input.
 490 DEF FN_name
 500 LOCAL name$,FLAG,n
 510 REPEAT
 520   FLAG=TRUE
 530   INPUT "Name ? " name$
 540   IF name$="" THEN 600
 550   FOR I=1 TO LEN(name$)
 560     n=ASC(MID$(name$,I,1))
 570     IF NOT(n=32 OR n>64 AND n<91 OR n>96 AND n<123) THEN FLAG=FALSE
 580  NEXT
 590   IF NOT FLAG THEN PRINT "No funny characters please !!!"
 600 UNTIL FLAG
 610 =name$
 620 :
 630 :
 640 REM Accept the age from the keyboard and
 650 REM round to one place of decimals. Ages of
 660 REM 0 or less or 150 or more are in error.
 670 :
 680 DEF FN_age
 690 LOCAL age
 700 REPEAT
 710   INPUT "What age ? " age
 720   IF age<=0 OR age >=150 THEN PRINT "No impossible ages please !!!"
 730 UNTIL age>0 AND age<150
 740 =INT(age*10+.5)/10
 750 :
 760 :
 770 REM Accept the height in centimetres from
 780 REM the keyboard and round to an integer.
 790 REM Heights of 50 or less or 230 or more
 800 REM are in error.
 810 DEF FN_height
 820 LOCAL height
 830 REPEAT
 840   INPUT "Height in centimetres ? " height
 850   IF height<=50 OR height>=230 THEN PRINT "Very funny !!!"
 860 UNTIL height>50 AND height<230
 870 =INT(height+.5)
 880 :
 890 :
 900 REM Accept the sex from the keyboard.  Only
 910 REM words beginning with upper or lower
 920 REM case M or F are valid.  The returned
 930 REM string is truncated to 1 character.
 940 DEF FN_sex
 950 LOCAL sex$,FLAG
 960 REPEAT
 970   FLAG=TRUE
 980   INPUT "Male or Female - M or F ? " sex$
 990   IF sex$<>"" THEN sex$=CHR$(ASC(MID$(sex$,1,1)) AND 95)
1000   IF sex$<>"M" AND sex$<>"F" THEN FLAG=FALSE
1010   IF NOT FLAG THEN PRINT "No more sex(es) please !!!"
1020 UNTIL FLAG
1030 =sex$

Compatible Data Files

The next example tackles the problem of writing files which will be compatible with other versions of BASIC. The most common format for serial files is as follows:

Data is written to the file as ASCII characters.
Data items are separated by commas.
Records are terminated by the two characters CR and LF.
The file is terminated by a Control Z (&1A).

The example program accepts data from the keyboard and writes it to a file in the above format.

Ex 7 - Writing a Compatible Data File

  10 REM F-WSTD
  20 :
  30 REM EXAMPLE OF WRITING A COMPATIBLE FILE
  40 :
  50 REM This program opens a file and writes
  60 REM numeric and character data to it in a
  70 REM compatible format.  Numerics are changed
  80 REM to strings before they are written and
  90 REM the data items are separated by commas.
 100 REM Each record is terminated by CR LF and
 110 REM the file is terminated by a Control Z.
 120 :
 130 REM Functions are used to accept and
 140 REM validate the data before writing it to
 150 REM the file.
 160 :
 170 record$=STRING$(100," "): REM Reserve room for the longest
 180 name$=STRING$(20," "): REM record necessary.
 190 : REM It saves on string space.
 200 compat=OPENOUT("COMPAT")
 210 PRINT "File Name COMPAT Opened as Handle ";compat
 220 PRINT
 230 REPEAT
 240   name$=FN_name
 250   IF name$="" THEN PROC_end
 260   age=FN_age
 270   height=FN_height
 280   sex$=FN_sex
 290   PRINT
 300   record$=name$+","+STR$(age)+","+STR$(height)+","+sex$
 310   PRINT#compat,record$
 320   BPUT#compat,&0A
 330 UNTIL FALSE
 340 :
 350 DEF PROC_end
 360 BPUT#compat,&1A
 370 CLOSE#compat
 380 END
 390 :
 400 :
 410 REM Accept a name from the keyboard and make
 420 REM sure it consists only of spaces and
 430 REM upper or lower case characters. Leading
 440 REM spaces are ignored on input.
 450 :
 460 DEF FN_name
 470 LOCAL name$,FLAG,n
 480 REPEAT
 490   FLAG=TRUE
 500   INPUT "Name ? " name$
 510   IF name$="" THEN 570
 520   FOR I=1 TO LEN(name$)
 530     n=ASC(MID$(name$,I,1))
 540     IF NOT(n=32 OR n>64 AND n<91 OR n>96 AND n<123) THEN FLAG=TRUE
 550   NEXT
 560   IF NOT FLAG THEN PRINT "No funny characters please !!!"
 570 UNTIL FLAG
 580 =name$
 590 :
 600 :
 610 REM Accept the age from the keyboard and
 620 REM round to one place of decimals.  Ages
 630 REM of 0 or less or 150 or more are
 640 REM considered to be in error.
 650 DEF FN_age
 660 LOCAL age
 670 REPEAT
 680   INPUT "What age ? " age
 690   IF age<=0 OR age >=150 THEN PRINT "No impossible ages please !!!"
 700 UNTIL age>0 AND age<150
 710 =INT(age*10+.5)/10
 720 :
 730 :
 740 REM Accept the height in centimetres from
 750 REM the keyboard and round to an integer.
 760 REM Heights of 50 or less and 230 or more
 770 REM are considered to be in error.
 780 DEF FN_height
 790 LOCAL height
 800 REPEAT
 810   INPUT "Height in centimetres ? " height
 820   IF height<=50 OR height>=230 THEN PRINT "Very funny !!!"
 830 UNTIL height>50 AND height<230
 840 =INT(height+.5)
 850 :
 860 :
 870 REM Accept the sex from the keyboard. Only
 880 REM words beginning with upper or lower
 890 REM case M or F are valid.  The returned
 900 REM string is truncated to 1 character.
 910 DEF FN_sex
 920 LOCAL sex$,FLAG
 930 REPEAT
 940   FLAG=TRUE
 950   INPUT "Male or Female - M or F ? " sex$
 960   IF sex$<>"" THEN sex$=CHR$(ASC(MID$(sex$,1,1)) AND 95)
 970   IF sex$<>"M" AND sex$<>"F" THEN FLAG=FALSE
 980   IF NOT FLAG THEN PRINT "No more sex(es) please !!!"
 990 UNTIL FLAG
1000 =sex$

Ex 8 - Reading a Compatible Data File

The last example in this section reads a file written in the above format and strips off the extraneous characters. The file is read character by character and the appropriate action taken. This is a simple example of how BBC BASIC (Z80) can be used to manipulate any CP/M-80 file by processing it on a character by character basis.

 10 REM F-RSTD
 20 :
 30 REM EXAMPLE OF READING A COMPATIBLE FILE
 40 :
 50 REM This program opens a data file and reads
 60 REM numeric and character data from it.  The
 70 REM data is read a byte at a time and the
 80 REM appropriate action taken depending on
 90 REM whether it is a character, a comma, or
100 REM a control char.
110 compat=OPENUP("COMPAT")
120 PRINT "File Name COMPAT Opened as Handle ";compat
130 PRINT
140 REPEAT
150   name$=FN_read
160   PRINT "Name ";name$
170   age=VAL(FN_read)
180   PRINT "Age ";age
190   height=VAL(FN_read)
200   PRINT "Height in centimetres ";height
210   sex$=FN_read
220   IF sex$="M" THEN PRINT "Male" ELSE PRINT "Female"
230   PRINT
240 UNTIL FALSE
250 :
260 :
270 REM Read a data item from the file.  Treat
280 REM commas and CRs as data item terminators
290 REM and Control Z as the file terminator.
300 REM Since we are not interested in reading a
310 REM record at a time, the record terminator
320 REM CR LF is of no special interest to us.
330 REM We use the CR, along with commas, as a
332 REM data item separator and discard the LF.
334 :
340 DEF FN_read
350 LOCAL data$,byte$,byte
360 data$=""
370 REPEAT
380   byte=BGET#compat
390   IF byte=&1A OR EOF#compat THEN CLOSE#compat: END
400   IF NOT(byte=&0A OR byte=&0D OR byte=&2C) THEN data$=data$+CHR$(byte)
410 UNTIL byte=&0D OR byte=&2C
420 =data$

CONTENTS

CONTINUE