DosQueryQueue
Queries the number of elements in a queue.
Syntax
#define INCL_DOSQUEUES #include <os2.h> HQUEUE hq; /* The handle of the queue to be queried. */ PULONG pcbEntries; /* A pointer to the number of elements in the queue. */ APIRET ulrc; /* Return Code. */ ulrc = DosQueryQueue(hq, pcbEntries);
Parameters
- hq (HQUEUE) - input
- The handle of the queue to be queried.
- pcbEntries (PULONG) - output
- A pointer to the number of elements in the queue.
Return Code
ulrc (APIRET) - returns
DosQueryQueue returns one of the following values:
- 0 NO_ERROR
- 337 ERROR_QUE_INVALID_HANDLE
Remarks
DosQueryQueue returns the number of elements that are currently in a queue. This function can be used by the server process and its threads, as well as by any client processes that have gained access to the queue by issuing DosOpenQueue.
If the server process closes the queue before this request is made, ERROR_QUE_INVALID_HANDLE is returned.
Example Code
This example shows how to create, write, query, and close a queue.
#define INCL_DOSQUEUES /* DOS Queue values */
#define INCL_DOSERRORS /* DOS Error values */
#include <os2.h>
#include <stdio.h>
#include <string.h>
#define QUE_NAME "\\QUEUES\\PANDAWRITE\\LOCALQUEUE"
int main(VOID) {
HQUEUE QueueHandle = NULLHANDLE; /* Queue handle */
CHAR *DataBuffer = ""; /* Data to write to queue */
ULONG ulNumElems = 0L; /* Number of elements on queue */
APIRET rc = NO_ERROR; /* Return code */
rc = DosCreateQueue(&QueueHandle, /* Queue handle */
QUE_LIFO | /* Last In, First Out ordering */
QUE_CONVERT_ADDRESS, /* Do 16-bit to 32-bit conversion */
QUE_NAME); /* Name of the queue */
if (rc!= NO_ERROR) {
printf ("DosCreateQueue error: return code = %u\n", rc);
return 1;
}
DataBuffer = "Element 1 of 2";
rc = DosWriteQueue (QueueHandle, 100L, strlen(DataBuffer),
(PVOID)DataBuffer, 0L);
if (rc!= NO_ERROR) {
printf ("DosWriteQueue error: return code = %u\n", rc);
return 1;
}
rc = DosQueryQueue (QueueHandle, &ulNumElems);
if (rc != NO_ERROR) {
printf ("DosQueryQueue error: return code = %u\n", rc);
return 1;
} else { printf ("DosQueryQueue: %u elements\n", ulNumElems); }
DataBuffer = "Element 2 of 2";
rc = DosWriteQueue (QueueHandle, 200L, strlen(DataBuffer),
(PVOID)DataBuffer, 0L);
if (rc!= NO_ERROR) {
printf ("DosWriteQueue error: return code = %u\n", rc);
return 1;
}
rc = DosQueryQueue (QueueHandle, &ulNumElems);
if (rc != NO_ERROR) {
printf ("DosQueryQueue error: return code = %u\n", rc);
return 1;
} else { printf ("DosQueryQueue: %u elements\n", ulNumElems); }
rc = DosPurgeQueue (QueueHandle);
if (rc != NO_ERROR) {
printf ("DosPurgeQueue error: return code = %u\n", rc);
return 1; }
rc = DosQueryQueue (QueueHandle, &ulNumElems);
if (rc != NO_ERROR) {
printf ("DosQueryQueue error: return code = %u\n", rc);
return 1;
} else { printf ("DosQueryQueue: %u elements\n", ulNumElems); }
rc = DosCloseQueue(QueueHandle); /* Close the queue */
if (rc!= NO_ERROR) {
printf ("DosCloseQueue error: return code = %u\n", rc);
return 1; }
return NO_ERROR;
}