VARPTR$ - QB64 Wiki

VARPTR$

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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 1: 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.


Example 2: 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.


Example 3: 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.


See also:



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