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extract a byte out of an integer

Posted on 2008-06-11
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Last Modified: 2010-04-21
Hi,

How do I extract a byte out of an integer. For example, I like to get the first byte of a 4-byte integer.
Thanks
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Question by:mycuti08
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6 Comments
 
LVL 40

Expert Comment

by:evilrix
ID: 21759102
>> For example, I like to get the first byte of a 4-byte integer.
Something like below...
int main()
{
	unsigned int dw = 0xFFEEDDCC;
	unsigned char byte0 = dw & 0xFF;
	unsigned char byte1 = (dw >> 8) & 0xFF;
	unsigned char byte2 = (dw >> 16)  & 0xFF;
	unsigned char byte3 = (dw >> 24) & 0xFF;
}

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LVL 40

Expert Comment

by:evilrix
ID: 21759137
Re: { http:#21759102 }

For each byte we need to use bitwise and (&) to mask in only 1 byte, we then just bit-shift 0, 8, 16 or 32 bits to the right so we can mask in byte 0, 1, 2 or 3 and exclude the rest. The bit-shift operators don't behave as you'd expect with signed types (they take into account the sign of the type and maintain it during shifting) so when doing bitwise arithmetic it is always best to use unsigned types.
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Accepted Solution

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evilrix earned 800 total points
ID: 21759153
You might find this tutorial helpful: http://www.cprogramming.com/tutorial/bitwise_operators.html
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Author Closing Comment

by:mycuti08
ID: 31466106
Thanks evilrix. It worked great
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LVL 40

Expert Comment

by:evilrix
ID: 21759180
>> Thanks evilrix. It worked great
Did you understand how/why it worked?
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Author Comment

by:mycuti08
ID: 21759486
yes I did.
Thanks evilrix
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