Use C language to get Hard Disk Serial Number in Linux

/*
* It gets the hard disk information in this case serial no.
* It uses ioctl() system call
*/
#include <stdio.h>
#include <string.h>
#include <linux/types.h>
#include <linux/hdreg.h>
#include <linux/fcntl.h>

//
int hd_serial(char *searial_no);
void trim(char *s);
//
int main() {
    char serial_no[256];

    if (hd_serial(serial_no)){
        printf("%s",serial_no);
    }

    return (0);
}
// ----------------------------------
int hd_serial(char *serial_no){
    int fd,err,i;

    /* structure to get disk information and
    * returned by HDIO_GET_IDENTITY, as per ANSI ATA2 rev.2f spec
    */
    struct hd_driveid hd;

    /* open the device */
    if( (fd=open("/dev/sda", O_RDONLY ) ) < 0 ){
        //perror("Device Open Error");
        return 0;
    }

    /* get required info */
    if( (err = ioctl(fd, HDIO_GET_IDENTITY, &hd) ) < 0){
        //perror("IOCTL err");
        return 0;
    }else{
        //printf("Serial No = %s\n",hd.serial_no);
        strcpy(serial_no, hd.serial_no);
        trim(serial_no);
        //printf("%s",serial_no);
    }
    return 1;
}
// ------------- trim  ---------------------------
void trim(char *s){
    int i=0, j, k, l=0;

    while((s[i]==' ')||(s[i]=='\t')||(s[i]=='\n'))
        i++;

    j = strlen(s)-1;
    while((s[j]==' ')||(s[j]=='\t')||(s[j]=='\n'))
        j--;

    if(i==0 && j==strlen(s)-1) { }
    else if(i==0) s[j+1] = '\0';
    else {
        for(k=i; k<=j; k++) s[l++] = s[k];
        s[l] = '\0';
    }
}
//----------------------------------------------

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;
}