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Top Forums Programming Generate Random Password in C Post 302203705 by jim mcnamara on Monday 9th of June 2008 02:52:53 PM
Old 06-09-2008
Here is a simple algorithm:
Code:
#include <stdlib.h>
#include <time.h>

static int srand_called=0;

char *random_pw(char *dest)
{
    size_t len=0;
    char *p=dest;
    int three_in_a_row=0;
    int arr[128]={0x0};

	/* be sure to have called srand exactly one time */
	if(!srand_called)
	{
		srandom(time(NULL));
		srand_called=1;
	}
	*dest=0x0; /* int the destination string*/
	for(len=6 + rand()%3; len; len--, p++) /* gen characters */
	{
		char *q=dest;
		*p=(rand()%2)? rand()%26 + 97: rand()%10 + 48;
		p[1]=0x0;
		arr[*p]++;                         /* check values */
		if(arr[*p]==3)
		{
			for(q=dest; q[2]>0 && !three_in_a_row; q++)	
				if(*q==q[1] && q[1]==q[2])
			   		three_in_a_row=1;
		}
		if(three_in_a_row || arr[*p]> 3 )
			return random_pw(dest);        /* values do not pass try again */
	}
    return dest;
}


Last edited by jim mcnamara; 06-11-2008 at 05:59 PM.. Reason: change srand to srandom
 

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STRCAT(3)						     Linux Programmer's Manual							 STRCAT(3)

NAME
strcat, strncat - concatenate two strings SYNOPSIS
#include <string.h> char *strcat(char *dest, const char *src); char *strncat(char *dest, const char *src, size_t n); DESCRIPTION
The strcat() function appends the src string to the dest string, overwriting the null byte ('') at the end of dest, and then adds a ter- minating null byte. The strings may not overlap, and the dest string must have enough space for the result. The strncat() function is similar, except that * it will use at most n characters from src; and * src does not need to be null-terminated if it contains n or more characters. As with strcat(), the resulting string in dest is always null-terminated. If src contains n or more characters, strncat() writes n+1 characters to dest (n from src plus the terminating null byte). Therefore, the size of dest must be at least strlen(dest)+n+1. A simple implementation of strncat() might be: char* strncat(char *dest, const char *src, size_t n) { size_t dest_len = strlen(dest); size_t i; for (i = 0 ; i < n && src[i] != '' ; i++) dest[dest_len + i] = src[i]; dest[dest_len + i] = ''; return dest; } RETURN VALUE
The strcat() and strncat() functions return a pointer to the resulting string dest. CONFORMING TO
SVr4, 4.3BSD, C89, C99. SEE ALSO
bcopy(3), memccpy(3), memcpy(3), strcpy(3), strncpy(3), wcscat(3), wcsncat(3) COLOPHON
This page is part of release 3.25 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. GNU
2008-06-13 STRCAT(3)
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