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Editorial Team
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Asked: 2026-05-28T18:27:29+00:00

I was looking through Expert C Programming by Peter Van Der Linden recently and

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I was looking through Expert C Programming by Peter Van Der Linden recently and came across this use for the += operator:

“If you have a complicated array reference and you want to demonstrate that the same index is used for both references, then:

node[i >> 3] += ~(0x01 << (i & 0x7));

is the way to go.”

As much as I’ve tried, I can’t figure out this code. I’m hoping someone here can explain what is actually going on and why it can be used to demonstrate that the same index is used?

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1 Answer

  1. Editorial Team

    My interpretation of the quote is that

    node[COMPLICATED_EXPRESSION] += STUFF;

    is preferable to 

    node[COMPLICATED_EXPRESSION] = node[COMPLICATED_EXPRESSION] + STUFF;

    since it’s easier to see at a glance what the intent is.

    More so if STUFF is also complicated, since this makes the overall expression even harder to parse at a glance.

    In the book, van der Linden explains where the code he shows came from:

    We took this example statement directly out of some
    code in an operating system. Only the data names have been changed
    to protect the guilty.

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