ZBasic System Library
205
ZBasic Microcontrollers
Type
Subroutine
Invocation
OpenQueue(queue, size)
OpenQueue(queue)
Parameter
Method
Type
Description
queue
ByRef
array of Byte
The queue to be initialized.
size
ByVal
int16
The size of the array, in bytes.
Discussion
This routine prepares a queue for use by initializing the management information contained in the queue
data structure. The number of bytes of space available for data in a queue is the specified size less the
queue management overhead (9 bytes). It may be convenient to use the built-in constant
System.MinQueueSize in the definition of an array intended to hold a queue.
If the compiler can deduce the size of the array element, e.g. an explicitly dimensioned Byte array is
specified, the second parameter may be omitted. In this case, the compiler utilizes the size of the array
as the size parameter. Otherwise, the compiler will issue an error message indicating that the size must
be explicitly specified.
Caution
If you specify a size parameter that is larger than the actual size of the array, data following the array may
be overwritten, usually with undesirable consequences. For this reason, it is recommended that you use
the SizeOf() function to specify the queue size so that it will automatically track any changes that you
make to the actual queue size. See the example below.
OpenQueue() should only be called for a queue that is not in use. Invoking it for a queue that is in use
has undefined results.
Example
Dim inQueue(1 to System.MinQueueSize + 20) as Byte
Call OpenQueue(inQueue, SizeOf(inQueue))
After the call to OpenQueue() the queue will ready to be used.
Compatibility
BasicX allows any type for the first parameter. The ZBasic implementation requires that it be an array of
Byte. The second parameter must always be supplied in BasicX mode.
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