#include <unistd.h>
#include <time.h>
#include <sys/time.h>
int rand_8(char *str)
{
    char  pool[] =  {'0','1','2','3','4','5','6','7','8','9', 'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z', 'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'};
    int i = 0;

    struct timeval tpstart;
    gettimeofday(&tpstart,NULL);
    srand(tpstart.tv_usec);        
    while(i != 8){
        str[i++] = pool[rand()%sizeof(pool)];
    }

    return 1;
}