VARPTR$ - QB64Official/qb64 GitHub Wiki

VARPTR$ is a memory function that returns a STRING representation of a variable's memory address value for use in a DRAW or PLAY statement.

Syntax

string_value$ = VARPTR$(variable)

Can use any STRING or numerical variable reference existing in memory.
If the parameter value is from an array it must be dimensioned already. Cannot use fixed length string arrays.
When using numerical variable values in DRAW strings, use an = sign after the function letter. "TA=" + VARPTR$(variable%)
Always use variable X as in "X" + VARPTR$(string_variable$) to DRAW or PLAY another STRING value.
DRAW relative Moves use a + or - before the equal sign. EX: DRAW "M+=" + VARPTR$(x%) + ",-=" + VARPTR$(y%)

Example(s)

How VARPTR$ reads consecutive values from memory.


SCREEN 2
CLS
WIND$ = "r10 d7 l10 u7 br20"   'create draw string to be read by function
ROW$ = "x"+VARPTR$(WIND$)+"x"+VARPTR$(WIND$)+"x"+VARPTR$(WIND$)+" x"+VARPTR$(WIND$)+"bl80 bd11"
LINE (100, 50)-(200, 160), , B
DRAW "bm 115,52"
FOR I = 1 TO 10
    DRAW "x" + VARPTR$(ROW$)
NEXT

NOTE:'GWBasic* allows semicolons to be used in the ROW$ definition, but QBasic and QB64 MUST use + concatenation.

Using the function to change a Turn Angle value using DRAW.


SCREEN 12
                           'Demonstrates how string DRAW angles are used with TA
FOR i = 0 TO 360 STEP 30           'mark clock hours every 30 degrees
  angle$ = STR$(i)                 'change degree value i to a string   
  PSET (175, 250), 6               'clock center
  DRAW "TA" + angle$ + "BU100"     'add string angle to Turn Angle and draw blind up
  CIRCLE STEP(0, 0), 5, 12         'place a circle at end of Up line
  DRAW "P9, 12"
  _DELAY .5           
NEXT
                            'Demonstrates how VARPTR$ is used with TA= 
DO: sec$ = RIGHT$(TIME$, 2)        'get current second value from time
  degree = VAL(sec$) * -6          'use a negative value to Turn Angle clockwise
  PSET (175, 250), 9               'clock center
  DRAW "TA=" + VARPTR$(degree) + "U90"  'VARPTR$ value requires = in DRAW
  DO: _LIMIT 30: LOOP UNTIL RIGHT$(TIME$, 2) <> sec$  'loop until seconds value changes
  IF INKEY$ <> "" THEN EXIT DO
  PSET (175, 250), 0
  DRAW "TA=" + VARPTR$(degree) + "U90"  'erase previous second hand draw
LOOP

Explanation: When the VARPTR$ value is used in DRAW, = MUST be used to pass the value to the draw! Negative Turn Angle values move clockwise and each second moves the hand 6 degrees. TA uses actual degree angles starting at 0 or noon.

Comparing DRAW moves using VARPTR$ and STR$ values.


SCREEN 12
PSET (200, 200), 12
CIRCLE STEP(0, 0), 5, 10
A = 100: B = 100
DRAW "M+=" + VARPTR$(A) + ",-=" + VARPTR$(B)

PSET (400, 400), 10
CIRCLE STEP(0, 0), 5, 12
C = 100: D = -100
DRAW "M+" + STR$(C) + "," + STR$(D) 'must add + for positive relative moves
END

Explanation: A negative STR$ value will move the DRAW relatively where VARPTR$ won't without the sign before the equal.

VARPTR$ - QB64Official/qb64 GitHub Wiki

Syntax

Example(s)

See Also