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The ctSysQueueMlen() function can be used to obtain the length of the next available message on the server-side queue (system queue). The syntax for ctSysQueueMlen() is:
ctCONV NINT ctDECL ctSysQueueMlen(NINT qhandle,LONG timeout)
Parameter qhandle is a system queue handle returned by a call to ctSysQueueOpen(). Parameter timeout specifies a time in milliseconds that ctSysQueueMlen() will block if the queue is empty. A timeout value of ctWAITFOREVER causes ctSysQueueMlen() to block until data is available in the queue. Use ctSysQueueMlen() to determine the appropriate size of a buffer before calling ctSysQueueRead(). ctSysQueueMlen() returns the length of the next available message, or a negative value on error.
Example
#include <ctreep.h>
int main(void)
{
NINT eRet = 0;
NINT hQueue = -1;
TEXT buffer[256];
NINT isam_init = 0;
NINT len;
/* init ISAM */
eRet = (NINT)INTISAMX(6, 7, 4, 6, 0, "ADMIN", "ADMIN", "FAIRCOMS");
if (eRet != NO_ERROR)
{
printf("INTISAM failed with error %d\n", eRet);
goto Exit;
}
isam_init++;
/* create a new queue */
hQueue = ctSysQueueOpen("MyQueue", 0);
if (hQueue < 0)
{
eRet = -hQueue;
printf("ctSysQueueOpen failed with error %d\n", eRet);
goto Exit;
}
/* write text to a queue using ctSysQueueWrite */
eRet = ctSysQueueWrite(hQueue, "This is the first line", 23);
if (eRet != NO_ERROR)
{
printf("ctSysQueueWrite failed with error %d\n", eRet);
goto Exit;
}
/* retrieve the size of the message in queue */
len = ctSysQueueMlen(hQueue, 100);
if (len < 0)
{
eRet = -len;
printf("ctSysQueueMlen failed with error %d\n", eRet);
goto Exit;
}
printf("Message length is %d\n", len);
/* check the len of the message */
if (len > sizeof(buffer))
{
printf("buffer is not large enough to receive message\n");
goto Exit;
}
eRet = ctSysQueueRead(hQueue, buffer, sizeof(buffer), ctWAITFOREVER);
/* check if read time-out */
if (eRet == NO_ERROR)
printf("Read: %s\n", buffer);
else if (eRet == NTIM_ERR)
printf("ctSysQueueRead time-out\n");
else
printf("ctSysQueueRead failed with error %d\n", eRet);
Exit:
/* close the queue */
if (hQueue >= 0)
{
eRet = ctSysQueueClose(hQueue);
if (eRet != NO_ERROR)
printf("ctSysQueueClose failed with error %d\n", eRet);
}
if (isam_init)
CLISAM();
return (int)eRet;
}
