ON TIMER(n)

The ON TIMER statement sets up a timed event to be repeated at specified intervals throughout a program when enabled.

Syntax

ON TIMER(seconds%) GOSUB {lineLabel|lineNumber}

ON TIMER([number%,] seconds!) { SUBprocedure | GOSUB {lineLabel|lineNumber} }

Description

Legacy syntax

• In the first syntax, the INTEGER seconds% parameter can be from 1 to 86400 seconds (one day).
• A TIMER ON statement must follow an ON TIMER event setup to initiate it.
• TIMER STOP disables timer events but remembers previous events when enabled again by a TIMER ON statement, and the recorded events may be executed immediately if a timer event has occurred.
• TIMER OFF disables timer event trapping. Events will not be remembered in a subsequent TIMER ON statement.
• ON TIMER events will interrupt a SLEEP call and RETURN to running program procedures.
• Only one TIMER event can be set at a time using this legacy syntax and all TIMER code must be in the main code, as it uses GOSUB.

QB64 syntax

• QB64 can use multiple numbered timer events and SINGLE floating point second values down to one millisecond (.001).
• The TIMER number% must be obtained from the _FREETIMER function. Store _FREETIMER numbers in a variable or an array to be able to reference them later.
• If the TIMER number is omitted or ON TIMER(0, seconds!) is used, then the TIMER used is the base TIMER (same as in the legacy syntax above).
• SUB procedures are allowed to be referenced, but CALL must not be used.
• SUB parameter values are passed by value and should be SHARED or literal values.
• Specific TIMER events can be turned on, suspended, turned off or freed using TIMER(n) ON, STOP, OFF or FREE.
• Use TIMER(n) FREE to release a timer event after it has been turned off or is no longer used.
  • The base TIMER cannot be freed.
• QB64 allows TIMER statements to also be inside of SUB and FUNCTION procedures.
• ON TIMER events will interrupt a SLEEP call and RETURN to running program procedures.
• $CHECKING:OFF can disable all QB64 event checking. Setting $CHECKING:OFF is only designed for 100% stable, error-less sections of code, where every CPU cycle saved counts.

QB64 Timing Alternatives

• The TIMER (function) can be used to find timed intervals down to 1 millisecond(.001) accuracy.
• The _DELAY statement can be used to delay program execution for intervals down to milliseconds.
• _LIMIT can slow down loops to a specified number of frames per second. This can also alleviate a program's CPU usage.

Examples

Example: Using a numbered TIMER to check the mouse button press status in QB64.

DIM SHARED Button AS LONG 'share variable value with Sub t1 = _FREETIMER 'get a timer number from _FREETIMER ONLY! ON TIMER(t1, .05) MouseClick TIMER(t1) ON DO LOCATE 1, 1 IF Button THEN PRINT "Mouse button"; Button; "is pressed."; ELSE PRINT SPACE$(70) END IF _DISPLAY LOOP UNTIL INKEY$ = CHR$(27) TIMER(t1) OFF TIMER(t1) FREE 'release timer END SUB MouseClick DO WHILE _MOUSEINPUT IF _MOUSEBUTTON(1) THEN COLOR 10: Button = 1 ELSEIF _MOUSEBUTTON(2) THEN COLOR 12: Button = 2 ELSE Button = 0 END IF LOOP END SUB

See also

• _FREETIMER, TIMER
• _DELAY, _LIMIT
• $CHECKING

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