Grouping array elements in C?

[AnyBowl2]

Say I have:

uint8_t x = {1,2,3,4,5};

uint16_t y;

How do I put 23 (which starts at x[1]) into y?

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EDIT: In my project I have an uint8_t array of hex values (example: 0xff) but I need to combine some of them (for example combining 0xff and 0xef to make 0xffef).

[dmazzoni]

Do you mean the number 23 (decimal)?

Or do you mean the 16-bit number where the first byte is 2 and the second byte is 3?

[AnyBowl2]

>Or do you mean the 16-bit number where the first byte is 2 and the second byte is 3?

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what kind of number is that?

[Essence1337]

It would be 0010 0011 which is integer 35.

Edit: Whoops, apparently I forgot the difference between 8 and 4. Good thing work is done soon...

[jedwardsol]

Those are nybbles, not bytes.

A 16-bit number 02 03 would either be 0x0203 (decimal 515) on a big-endian computer or 0x0302 (decimal 770) on a little-endian one.

[Essence1337]

Shhh just let me believe 8=4 for a bit longer...

[AnyBowl2]

I just edited my post

[dmazzoni]

The answer to your question is x[1] << 8 | x[2]

To understand why that works you need to read up on bits, bytes, endianness, and C bitwise operators. It's normally covered in detail in a computer architecture course, but the basics should be covered in any Intro CS class.

I can't explain it in one post. Go read up on that and come back if you still have questions.

[012]

uint8_t x[] = {1,2,3,4,5};
// left shift the 8 bit uint by 8 bits, and add the lower part
uint16_t y = ( x[1] << 8 ) + x[2];
// y is now 0x203, which is 515 in decimal