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Full Discussion: does any one know how to solve?
Top Forums Programming does any one know how to solve? Post 302228872 by redoubtable on Monday 25th of August 2008 05:29:20 PM
Old 08-25-2008
Quote:
Originally Posted by shamrock
The problem with static cases is that you are restricted in the size of the database that can be created. Declaring a 1000 element array implies that the database can't have more than 1000 records in it atleast there is no easy way to alter the number of records it can have short of modifying the array definition in the source code and re-compiling.
Sure. For the situation at hand static cases should only be used if performance really matters. If there is a need to expand the number of entries to an unknown value we should use dynamic algorithms (linked list implementation for example)

Quote:
the sizeof operator returns the allocated size instead of the used size for any object...so in the above case it will return the "sizeof one empRec structure times 10".
Thus confirming that your initial solution can't be used in both static/dynamic cases like I said. If you have a static case that needs expanding sizeof() will not help to determine the number of entries and if you have a dynamic case sizeof() will not help too.

Quote:
Determine the size of one empRec structure and malloc'ate memory for it before adding a new record. This way the database size is not limited by the number of elements in the array.
The code snippet below can be put inside a loop to allocate space for a block of at least empRec size bytes followed by prompting the user for input and storing it in one of the elements of the empRec structure members.

Code:
pointer_to_empRec_object = malloc(sizeof(struct empRec));

while () {    /* while loop to capture user input */
    printf("get emp name ");
    fgets()   /* store emp name input above */
    printf("get emp room ");
    fgets()   /* store emp room */
    printf("get emp start date ");
    fgets()   /* store emp start date */
}   /* end of while loop */

Remember that we're talking about an array of structs so either we use linked lists or we would have to malloc() a pointer of pointers to struct empRec.

Anyway I was just saying that the initial solution you posted will fit best in static cases which don't need expansion because you used sizeof() to calculate the number of entries and that wouldn't be possible if there were more entries in the array struct than those in use.
 

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LEARN ABOUT HPUX

insq

insq(9F)						   Kernel Functions for Drivers 						  insq(9F)

NAME

       insq - insert a message into a queue

SYNOPSIS

       #include <sys/stream.h>

       int insq(queue_t *q, mblk_t *emp, mblk_t *nmp);

INTERFACE LEVEL

       Architecture independent level 1 (DDI/DKI).

PARAMETERS

       q	Pointer to the queue containing message emp.

       emp	Enqueued message before which the new message is to be inserted. mblk_t is an instance of the msgb(9S) structure.

       nmp	Message to be inserted.

DESCRIPTION

       insq()  inserts a message into a queue. The message to be inserted, nmp, is placed in q immediately before the message emp. If emp is NULL,
       the new message is placed at the end of the queue. The queue class of the new message is ignored. All flow control parameters are  updated.
       The service procedure is enabled unless QNOENB is set.

RETURN VALUES

       insq() returns 1 on success, and 0 on failure.

CONTEXT

       insq() can be called from user or interrupt context.

EXAMPLES

       This routine illustrates the steps a transport provider may take to place expedited data ahead of normal data on a queue (assume all M_DATA
       messages are converted into M_PROTO T_DATA_REQ messages). Normal T_DATA_REQ messages are just placed on the end of  the	queue  (line  16).
       However,  expedited  T_EXDATA_REQ  messages  are inserted before any normal messages already on the queue (line 25). If there are no normal
       messages on the queue, bp will be NULL and we fall out of the for loop (line 21). insq acts like putq(9F) in this case.

	     1	#include
	     2	#include
	     3
	     4	static int
	     5	xxxwput(queue_t *q, mblk_t *mp)
	     6	{
	     7	 union T_primitives *tp;
	     8	 mblk_t *bp;
	     9	 union T_primitives *ntp;
	    10
	    11	 switch (mp->b_datap->db_type) {
	    12	 case M_PROTO:
	    13	      tp = (union T_primitives *)mp->b_rptr;
	    14	      switch (tp->type) {
	    15	      case T_DATA_REQ:
	    16		      putq(q, mp);
	    17		      break;
	    18
	    19	      case T_EXDATA_REQ:
	    20		      /* Insert code here to protect queue and message block */
	    21		      for (bp = q->q_first; bp; bp = bp->b_next) {
	    22			 if (bp->b_datap->db_type == M_PROTO) {
	    23			   ntp = (union T_primitives *)bp->b_rptr;
	    24			   if (ntp->type != T_EXDATA_REQ)
	    25			       break;
	    26			}
	    27		      }
	    28		      (void)insq(q, bp, mp);
	    29		      /* End of region that must be protected */
	    30		      break;
		      . . .
	    31		    }
	    32	 }
	    33	}

       When using insq(), you must ensure that the queue and the message block is not modified by another thread at the same time. You can achieve
       this either by using STREAMS functions or by implementing your own locking.

SEE ALSO

       putq(9F), rmvq(9F), msgb(9S)

       Writing Device Drivers

       STREAMS Programming Guide

WARNINGS

       If emp is non-NULL, it must point to a message on q or a system panic could result.

SunOS 5.10							    9 Jul 2001								  insq(9F)
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