How to store CHAR array to string MAC ADDRESS

Question

I have a function that returns a unsigned char chMAC[6]; which is the mac address and i print it out as

printf("Mac: %x",chMAC[0]);
printf("%x",chMAC[1]);
printf("%x",chMAC[2]);
printf("%x",chMAC[3]);
printf("%x",chMAC[4]);
printf("%x\n",chMAC[5]);

And i get an output as Mac: B827E82D398E which is the actual mac address, but now i need to get that value as a string to pass to a sql parameter and i don't know how, since i need to add : in between. such as Mac: B8:27:E8:2D:39:8E

i bet this is easy, but i am still learning C.

Look at sprintf(), or better yet, snprintf().

Andrew Henle
– Andrew Henle

2015-08-31 21:51:28 +00:00
Commented Aug 31, 2015 at 21:51 — Andrew Henle
– Andrew Henle, Commented Aug 31, 2015 at 21:51

Doug Currie · Accepted Answer · 2015-08-31 21:53:47Z

3

You probably want all the bytes to be displayed as two characters:

%2x

but with a leading 0 instead of space:

%02x

You can string this all together in one printf call

printf("Mac: %02X:%02X:%02X:%02X:%02X:%02X\n"
       , chMAC[0], chMAC[1], chMAC[2], chMAC[3], chMAC[4], chMAC[5]);

If you want the text to go to a sting buffer instead of stdout do this:

char buffer[32];

snprintf(buffer, sizeof(buffer)
        , "Mac: %02X:%02X:%02X:%02X:%02X:%02X\n"
        , chMAC[0], chMAC[1], chMAC[2], chMAC[3], chMAC[4], chMAC[5]);

answered Aug 31, 2015 at 21:53

Doug Currie

41.4k1 gold badge103 silver badges121 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Erik Johnson · Accepted Answer · 2015-08-31 22:04:36Z

3

You have all the pieces there, you just need to string them into the right order. Instead of using 6 separate printf() statements, pull it into one statement with all the formatting:

printf("Mac: %02X:%02X:%02X:%02X:%02X:%02X\n", 
             chMAC[0], chMAC[1], chMAC[2], chMAC[3], chMAC[4], chMAC[5]);

The "02" in the "%02X" formatting statements will put a leading zero if the value is <15; the capital X will make the alphabetic Hex digits into capitals (which is the usual convention when passing MAC addresses).

To send the resulting string to a buffer instead of to stdout, call sprintf (or even better, snprintf) with the same formatting string.

char mac_str[24];
snprintf(mac_str, sizeof(mac_str), "Mac: %02X:%02X:%02X:%02X:%02X:%02X\n", 
              chMAC[0], chMAC[1], chMAC[2], chMAC[3], chMAC[4], chMAC[5]);

edited Aug 31, 2015 at 22:04

answered Aug 31, 2015 at 21:53

Erik Johnson

1,1746 silver badges18 bronze badges

1 Comment

Barmar Over a year ago

He asked how to store it in a string, not how to print it.

Marc B · Accepted Answer · 2015-08-31 22:01:09Z

0

why all the separate calls?

newlength = sprintf(mac, '%x:%x:%x:%x:%x:%x\n', chMAC[1], etc....)

You can have multiple %whatever format characters in a single printf/sprintf call...

edited Aug 31, 2015 at 22:01

answered Aug 31, 2015 at 21:53

Marc B

362k44 gold badges433 silver badges508 bronze badges

3 Comments

pato.llaguno Over a year ago

i read the documentation on sprintf but it retunres the number of displayed chars,

If successful, the total number of characters written is returned excluding the null-character appended at the end of the string, otherwise a negative number is returned in case of failure.

Barmar Over a year ago

You're missing the output buffer argument.

Marc B Over a year ago

yeah, sorry. been buried in php-land too long. fixing up the sample.

Collectives™ on Stack Overflow

How to store CHAR array to string MAC ADDRESS

3 Answers 3

Comments

1 Comment

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

1 Comment

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related