Using MD5 in C language

http://mixtt.blogspot.com/2009/06/c-using-md5-in-c-language.html

#include <openssl/md5.h>
/*Encode str to str_enc using md5 algorithm*/
void md5(char *str, char *str_enc) {
    int i = 0;
    unsigned char d[16];
    MD5_CTX ctx;
    MD5_Init(&ctx);
    MD5_Update (&ctx, (char *) str, strlen(str));
    MD5_Final(d, &ctx);
    for (i = 0; i < 16; i++) {
        sprintf(str_enc + (i*2), "%02X", d[i]);
    }
    str_enc[32] = 0;
}

Use C language to get MAC Address in linux

#include <stdio.h>
#include <string.h> /* for strncpy */
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <netinet/in.h>
#include <net/if.h>

int main(void) {
    int fd;
    struct ifreq ifr;

    char mac[20];
    fd = socket(AF_INET, SOCK_DGRAM, 0);

    ifr.ifr_addr.sa_family = AF_INET;
    strncpy(ifr.ifr_name, "eth0", IFNAMSIZ-1);

    ioctl(fd, SIOCGIFHWADDR, &ifr);

    close(fd);

    sprintf(mac,"%.2x:%.2x:%.2x:%.2x:%.2x:%.2x",
         (unsigned char)ifr.ifr_hwaddr.sa_data[0],
         (unsigned char)ifr.ifr_hwaddr.sa_data[1],
         (unsigned char)ifr.ifr_hwaddr.sa_data[2],
         (unsigned char)ifr.ifr_hwaddr.sa_data[3],
         (unsigned char)ifr.ifr_hwaddr.sa_data[4],
         (unsigned char)ifr.ifr_hwaddr.sa_data[5]);

    printf("eth0 mac address:%s\n", mac);

    return 0;
}