sprintf issue

[someprogr]

I'm trying to write a basic function that converts a 6 byte array to a formatted mac address string:

i.e. 0x12 0x13 0x14 0x15 0x16 0x17

would be formatted to:

12:13:14:15:16:17

The code I wrote was as follows:

char buffer[100];
char mac[] = { 0x12, 0x13, 0x14, 0x15, 0x16, 0x17 };

sprintf(buffer, "%.2x:%.2x:%.2x:%.2x:%.2x:%.2x", mac[0],mac[1],mac[2],mac[3],mac[4],mac[5]);

It appears to partially work. Here is the contents of buffer in memory after its executed:

buf = 0x003ffd58 "12:13:14:15:16:17"

This is correct! Ok. But if I try mac as a different array:

mac = { 0x35, 0xaa, 0x11, 0xed, 0x71, 0xac };

I get:

buf = 0x0028fd54 "35:ffffffaa:11:ffffffed:71:ffffffac"

How do I get rid of all those f's?

[bsattin1]

it looks as though your "characters" are being sign-extended.

Notice how you only get an issue when trying with numbers 8 or higher.

the answer is to make your array unsigned chars.

Hope this helps!

[CommonTater]

Have you tried it without the ".2" modifiers?

Also you should define your mac array as unsigned char mac[6]; to prevent values greater than 0x7f from being represented as negative numbers.

[CommonTater]

it looks as though your "characters" are being sign-extended.

Notice how you only get an issue when trying with numbers 8 or higher.

the answer is to make your array unsigned chars.

Hope this helps!

LOL ... I see you beat me to it.

[bsattin1]

just started answering questions today...I gotta fight for my posts

[CommonTater]

just started answering questions today...I gotta fight for my posts

Oh gosh, you mean it's a contest?
Looks like I missed yet another memo...

LOL!