_EXIT (function)

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Revision as of 02:38, 28 January 2016 by imported>Clippy
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The _EXIT function prevents a program user exit and indicates if a user has clicked the close X window button or CTRL + BREAK.


quit% = _EXIT


  • Once the _EXIT function is used, the program user can no longer manually exit the program until it ends.
  • _EXIT returns any exit requests made AFTER the initial call as:
0 = no exit request has been made since EXIT monitoring began in the program.
1 = exit attempted by clicking the window X (close) box since last function call. (Bit 0 set)
2 = exit attempted with CTRL + BREAK since last call. (Bit 1 set)
3 = both CTRL + BREAK and the X box have been used since last call. (Bit 0 and 1 set)
  • If a return value is not 0 the program can handle an exit request at a more convenient time if necessary.
  • After a read, the _EXIT value is reset to 0 so store the value when a program delays an exit request.
  • Note: Once _EXIT has been used once, you MUST monitor your program by checking it for user EXIT requests!
  • Don't just use _EXIT once to prevent a user from exiting a program early! The user may NOT appreciate that!

Example 1: Using an ON TIMER check to read the _EXIT request return values.

q = _EXIT 'function read prevents any program exit at start of program ON TIMER(5) GOSUB quit TIMER ON PRINT " The Timer will check for exit request every 5 seconds." PRINT "Click the X box and/or Ctrl - Break to see the _EXIT return!" PRINT " Any Key Quits" PRINT DO: _LIMIT 30 ' ' simulated program loop LOOP UNTIL INKEY$ <> "" END quit: q = _EXIT IF q THEN PRINT q; SELECT CASE q CASE 1: PRINT "= X button was clicked" CASE 2: PRINT "= Ctrl + Break keypress" CASE 3: PRINT "= Both X and Ctrl + Break!" END SELECT RETURN

Example 2: Removing temporary files before closing a program upon a user's exit request.

x = _EXIT 'initial function call blocks a user exit OPEN "t3mpdata.tmp" FOR APPEND AS #1 DO IF _EXIT THEN CLOSE: KILL "t3mpdata.tmp": _DELAY 1: SYSTEM LOOP

Note: If you have a file named t3mpdata.tmp change the file name!

See also

  • SYSTEM (ends a program immediately and closes the window in QB64 or a Qbasic program run from the command line, not IDE.)
  • END (ends a program displaying "Press any key to continue...".)
  • EXIT (exits a loop, SUB or FUNCTION when used before DO, FOR, WHILE, SUB or FUNCTION)

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