用按位运算符检查字节

Question

I could use this:

unsigned long alpha = 140 | 130 << 8 | 255 << 16;

to set 140 to the first byte of alpha , 130 to the second and 255 as 3rd. How do I do the opposite (ie checking a specific byte of alpha ) ?

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alpha & 255 // works for the first byte
alpha >> 16; // works for the 3rd byte

Answer 1

Shift the value x bits to the right and then use AND to restrict the number of bits you use. ie: (n >> 8) & 0xff or (n >> 16) & 0xff .