Why is my string getting trounced?

hinv · 2010-11-23 22:11

Hi,

I found a problem with my program that I cannot figure out. I admittedly don't have a good grasp of the scope of variables in spin, so that may be it, but in the below code dstring keeps getting set to what I type in through the getline function. Any help would be appreciated.

OBJ
  ser   : "FullDuplexSerial"
  dt    : "datatransfer"        ' The datatransfer object
  key   : "combokeyboard"
  lcd   : "jm_lcd4_ez"

PUB Start | time, okay, ofreq, duty, seconds, period, ontime, offtime, whole, frac, dstring

  ''Test Parallax Serial Terminal number entry and display.
  ser.start(31, 30, 0, 9600)

  ''start the keyboard
  key.start(26)
  dira[enable]~~                 'set the enable pin direction (pin 1 on LM293)

  ''Start the LCD
  okay := lcd.init(0, 16, 1)


  repeat
    ser.tx(13)
    dstring := String("0.00")
    repeat until ofreq > 99 and ofreq < 50_000_01
      ser.str(String("Frequency: "))
      lcd.scrollstr(1, 1, 16, 250, @askfreq)
      lcd.moveto(12,1)
      lcd.cursor(2)
      dstring := getline
      ser.str(String("Dstring: "))
      ser.str(dstring)
      ser.dec(StrLen(dstring))
      ser.tx(13)
      ofreq := StrToFreq(dstring)
      ser.str(String("Ofreq: "))
      ser.Dec(ofreq)
      ser.tx(13)
    repeat until duty > 4 and duty < 96
      ser.str(String("Duty: "))
      lcd.scrollstr(1, 1, 16, 250, @askduty)
      lcd.moveto(15,1)
      lcd.cursor(2)
      duty := StrToDec(getline)
    repeat until seconds > 0 and seconds < 601
      ser.str(String("Seconds: "))
      lcd.scrollstr(1, 1, 16, 250, @asksecs)
      lcd.moveto(14,1)
      lcd.cursor(2)

      ''why is dstring getting set to what I type in for duty?
      ser.str(String("Dstring: "))
      ser.str(dstring)
      ser.tx(13)

      seconds := StrToDec(getline)

      ''why is dstring getting set to what I type in for seconds?
      ser.str(String("Dstring: "))
      ser.str(dstring)
      ser.tx(13)

PRI getline | i, c
   i := 0
   repeat
      'repeat while (c := ser.rxcheck) < 0               'use serial
      c := key.getkey                                  'use keyboard
      if c == Bsp
         if i > 0
            ser.tx(8)           'send a real backspace
            i--
      elseif c == Cr
         ser.tx(c)           ' If serial console, use CR/LF
         ser.tx(Lf)
         tline[i] := 0
         tp := @tline
         return tp
      elseif i < linelen-1
         ser.tx(c)
         lcd.out(c)
         tline[i++] := c

PUB StrToDec(stringptr) : value | char, index

    '' Converts a zero terminated string representation of a decimal number to a value

    value := index := 0
    repeat until ((char := byte[stringptr][index++]) == 0)
       if char => "0" and char =< "9"
          value := value * 10 + (char - "0")
    if byte[stringptr] == "-"
       value := - value

Mike Green · 2010-11-23 22:21

You're not showing everything.

Remember that "getline" always returns the address of "tline" where the input line gets stored. Each time you call "getLine", the array "tline" gets used again and changed to whatever you enter.

When you assign "getline" to something else like "dstring", you're only making a copy of the address of the string (in "tline"), not a copy of the string itself.

wjsteele · 2010-11-24 08:43

You'll need to use one of the copy commands [bytecopy] to copy the string into your buffer instead of just assigning the variable.

Assigning the variable, like Mike says, is just copying the address... so in essense, you're overwriting the same memory space for all three instances of where you use it.

If you use something like bytecopy(@ofreq, @dstring, StrSize(@dstring)) you'll get a better result. Don't forget, you'll have to allocate enough space in ofreq to hold the new string, however.

Bill

hinv · 2010-11-24 20:14

Yep, that's got to be it. I really didn't think through the string thing.

Attached is the full code. It works great using the serial port and the external numeric keypad.
I'm just trying to get a status screen working on the LCD to finish it up.

hinv · 2010-11-24 22:37

Anybody know a good tutorial or example of handling strings in spin?

EmptyBit · 2010-12-03 13:24

I was looking for tutorials myself and had not found any directly, although in the OBEX there are some great d/l's that show how strings are spin-nipulated. Should be good enough to use the concepts for many circumstances within your own code.

http://obex.parallax.com/objects/23/
http://obex.parallax.com/objects/502/
http://obex.parallax.com/objects/529/

$0

Why is my string getting trounced?

Comments