Product Documentation

FairCom ISAM for C

Previous Topic

Next Topic

Retrieving the Size of the Next Message in a Server-Side Queue

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.


#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;



/* 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");


printf("ctSysQueueRead failed with error %d\n", eRet);


/* close the queue */

if (hQueue >= 0)


eRet = ctSysQueueClose(hQueue);

if (eRet != NO_ERROR)

printf("ctSysQueueClose failed with error %d\n", eRet);


if (isam_init)


return (int)eRet;