random filename

randomize.c

/*
 * randomize.c -- generate random file name
 * Author: Krzysztof Krolikowski <kkrolikowski@gamil.com>
 * compilation:
 * gcc -o randomize randomize.c
 * running:
 *  ~$ ./randomize
 *  dyndns_nBXGV0cW
 *
 */
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <string.h>

int main(void) {
        char * entropy = "1qaz2wsx3edc4rfv5tgb6yhn7ujm8i0poklaZAQ1XSW2CDE3VFR4BGT5NHY6MJU6MJU7";
        int n, i;
        const int len = 8;                              // random part lenght
        struct timeval tv;
        char tmp[15] = "dyndns_";                       // prefix of temp file
        char * ptmp;                                    // pointer to the begining of temp filename
        ptmp = tmp + strlen(tmp);                       // moving to the end of a prefix

        for(i=0; i<len; i++, ptmp++) {                  // while counter is smaller then lenght of random part
                gettimeofday(&tv, NULL);                // get current time
                srand(tv.tv_usec);                      // generate new seed with time in micro seconds
                n = rand() % strlen(entropy);           // generate new random character
                *ptmp = entropy[n];                     // and put it in the next field of an array.
        }
        *ptmp = '\0';                                   // end of string containing random filename
        puts(tmp);

        return 0;
}