How do I extract specific 'n' bits of a 32-bit unsigned integer in C?

Question

Could anyone tell me as to how to extract \'n\' specific bits from a 32-bit unsigned integer in C.

For example, say I want the first 17 bits of the 32-bit value;

Answer 1

Bitwise AND your integer with the mask having exactly those bits set that you want to extract. Then shift the result right to reposition the extracted bits if desired.

unsigned int lowest_17_bits = myuint32 & 0x1FFFF;
unsigned int highest_17_bits = (myuint32 & (0x1FFFF << (32 - 17))) >> (32 - 17);

Edit: The latter repositions the highest 17 bits as the lowest 17; this can be useful if you need to extract an integer from “within” a larger one. You can omit the right shift (>>) if this is not desired.