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Full Discussion: generating 16 digit random number in C
Top Forums Programming generating 16 digit random number in C Post 302344140 by jim mcnamara on Friday 14th of August 2009 04:48:31 PM
Old 08-14-2009
Another thought - not all unixes have /dev/urandom and /dev/random.
You can read abou them, but they do provide a random bitstream. If your box has them (Soalris & Linux come to mind) read on -

An example of how to play with the bitstream using Corona's idea.:
Code:
#include <stdio.h>

typedef
union
{
	char tmp[sizeof(unsigned long long)];
	unsigned long long myll;
} ll_t;


unsigned long long llrand(void)
{
	FILE *in=fopen("/dev/urandom", "r");
	ll_t ll_u;
	fread(ll_u.tmp, sizeof(ll_u.tmp), 1, in);
	fclose(in);
	return ll_u.myll;
}

int main()
{
	char tmp[64]={0x0};
	char working[64]={0x0};
	int i=0;
		
	for(i=0; i< 20; i++)
	{
		while(strlen(tmp) < 16)
		{
			sprintf(working, "%lu", llrand() );
			strcat(tmp, working);
		}
		tmp[16]=0x0;
		printf("%s\n", tmp);
		*tmp=0x0;
	}
	return 0;
}

This needs work but you get the idea.
 

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LEARN ABOUT OPENSOLARIS

rmvb

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

NAME

       rmvb - remove a message block from a message

SYNOPSIS

       #include <sys/stream.h>

       mblk_t *rmvb(mblk_t *mp, mblk_t *bp);

INTERFACE LEVEL

       Architecture independent level 1 (DDI/DKI).

PARAMETERS

       mp    Message from which a block is to be removed. mblk_t is an instance of the msgb(9S) structure.

       bp    Message block to be removed.

DESCRIPTION

       The  rmvb()  function  removes a message block (bp) from a message (mp), and returns a pointer to the altered message. The message block is
       not freed, merely removed from the message. It is the module or driver's responsibility to free the message block.

RETURN VALUES

       If successful, a pointer to the message (minus the removed block) is returned. The pointer is NULL if bp was the only block of the  message
       before  rmvb() was called. If the designated message block (bp) does not exist, -1 is returned.

CONTEXT

       The rmvb() function can be called from user, interrupt, or kernel context.

EXAMPLES

       This  routine  removes  all  zero-length M_DATA message blocks from the given message. For each message block in the message, save the next
       message block (line 10). If the current message block is of type M_DATA and has no data in its buffer (line 11), then remove  it  from  the
       message (line 12) and free it (line 13). In either case, continue with the next message block in the message (line 16).

	 1  void
	  2  xxclean(mp)
	  3	 mblk_t *mp;
	  4  {
	  5	     mblk_t *tmp;
	  6	     mblk_t *nmp;
	  7
	  8	     tmp = mp;
	  9	     while (tmp) {
	 10		      nmp = tmp->b_cont;
	 11		      if ((tmp->b_datap->db_type == M_DATA) &&
				    (tmp->b_rptr == tmp->b_wptr)) {
	 12			   (void) rmvb(mp, tmp);
	 13			   freeb(tmp);
	 14		      }
	 15		      tmp = nmp;
	 16	     }
	 17  }

SEE ALSO

       freeb(9F), msgb(9S)

       Writing Device Drivers

       STREAMS Programming Guide

SunOS 5.11							    16 Jan 2006 							  rmvb(9F)
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