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.