iOS7以下设备获取mac地址

#include <sys/socket.h>
#include <sys/sysctl.h>
#include <net/if.h>
#include <net/if_dl.h>

NSString *  macaddress();

#import "MacAddress.h"

NSString *  macaddress()
{
int                    mib[6];
size_t                 len;
char                  *buf;
unsigned char         *ptr;
struct if_msghdr      *ifm;
struct sockaddr_dl    *sdl;

mib[0] = CTL_NET;
mib[1] = AF_ROUTE;
mib[2] = 0;
mib[3] = AF_LINK;
mib[4] = NET_RT_IFLIST;

if ((mib[5] = if_nametoindex("en0")) == 0)
{
printf("Error: if_nametoindex error/n");
return NULL;
}

if (sysctl(mib, 6, NULL, &len, NULL, 0) < 0)
{
printf("Error: sysctl, take 1/n");
return NULL;
}

if ((buf = malloc(len)) == NULL)
{
printf("Could not allocate memory. error!/n");
return NULL;
}

if (sysctl(mib, 6, buf, &len, NULL, 0) < 0)
{
printf("Error: sysctl, take 2");
return NULL;
}

ifm = (struct if_msghdr *)buf;
sdl = (struct sockaddr_dl *)(ifm + 1);
ptr = (unsigned char *)LLADDR(sdl);

NSString *outstring = \
[NSString stringWithFormat:@"%02x%02x%02x%02x%02x%02x",
*ptr,     *(ptr+1), *(ptr+2),
*(ptr+3), *(ptr+4), *(ptr+5)];

free(buf);

return [outstring uppercaseString];
}