Creating a char array using hex values

Question

I've got a quick question to someone that knows their way around C - I'm trying to save a char array using hex values, so it looks like this :

char string[84]={0x32,0x51,0x0b,0xa9,0xba,0xbe,0xbb,0xbe,0xfd,0x00,0x15,0x47,0xa8,0x10,0xe6,0x71,0x49,0xca,0xee,0x11,0xd9,0x45,0xcd,0x7f,0xc8,0x1a,0x05,0xe9,0xf8,0x5a,0xac,0x65,0x0e,0x90,0x52,0xba,0x6a,0x8c,0xd8,0x25,0x7b,0xf1,0x4d,0x13,0xe6,0xf0,0xa8,0x03,0xb5,0x4f,0xde,0x9e,0x77,0x47,0x2d,0xbf,0xf8,0x9d,0x71,0xb5,0x7b,0xdd,0xef,0x12,0x13,0x36,0xcb,0x85,0xcc,0xb8,0xf3,0x31,0x5f,0x4b,0x52,0xe3,0x01,0xd1,0x6e,0x9f,0x52,0xf9,0x04};

so basically when I output it using for example something like

for (i=0;i<string_len;i++)
        printf("%d \t---\t %x\n",i,cipher_11[i]);

I'd expect to get the same values, just without the 0x in front and it does work for most of those values, some of them however have "ffff" in front which kind of breaks the rest of my program :) Kind of a newbie in hex operations so I'm pretty sure I'm doing something very silly. Any hints ? (btw the output looks like the picture : http://postimg.org/image/k0npwh9a5/ )

paddy · Accepted Answer · 2014-01-19 23:33:45Z

5

Some of your characters have their most significant bit set, and so would represent a negative value (assuming your compiler treats char as a signed value). So when it is implicitly cast as an integer (during the call to printf), it will be interpreted as a negative value. This is the case for all values larger than 0x7f.

You should either declare cipher_11 as unsigned char, or cast the value during printf:

printf("%d \t---\t %x\n", i, (unsigned char)cipher_11[i]);

answered Jan 19, 2014 at 23:33

paddy

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1 Comment

Errtu Over a year ago

thanks a lot for the quick reply, that does solve the issue :). I was thinking it might have something to do with negative numbers, just wasn't sure how to get around that. declaring the value as unsigned char does exactly what I want - in dev c++ at least :).

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