From QB64 Wiki
Revision as of 12:59, 19 October 2010 by imported>Clippy
Jump to navigation Jump to search

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 reference values in DRAW strings, use an = sign after the function letter. "TA=" + VARPTR$(value)
  • DRAW and PLAY can use the substring value after "X" + VARPTR$(value) to draw or play another string.

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.

See also:

Keyword Reference - Alphabetical
Keyword Reference - By Usage
Main Wiki Page