CODEWITHSUNDEEP
cbitwise-operatorsoperator-precedence
poida
poida

Reputation: 3599

Operator precedence (bitwise '&' lower than '==')

In the C programing language, why do the bitwise operators (& and |) have lower precedence than the equality operator (==)? It does not make sense to me.

Upvotes: 51

Views: 7660

Answers (3)

Michael Cornelius
Michael Cornelius

Reputation: 1564

It doesn't make sense to Dennis Ritchie, either, in retrospect.

&& and || were added to the language after | and &, and precedence was maintained for reasons of compatibility.

Upvotes: 19

Caladain
Caladain

Reputation: 4934

You need to ask Brian Kernighan or Dennis Ritchie.
From the forum post Operator precedence:

The && and || operators were added later for their "short-circuiting" behavior. Dennis Ritchie admits in retrospect that the precedence of the bitwise operators should have been changed when the logical operators were added. But with several hundred kilobytes of C source code in existence at that point and an installed base of three computers, Dennis thought it would be too big of a change in the C language...

So, that might be a reason? I'm guessing since there are several layers of bitwise precedence (unlike relational comparisons) that it's cruft that's existed since...forever...and just was never corrected.

Upvotes: 57

templatetypedef
templatetypedef

Reputation: 373112

I don't have an authoritative answer as to why K&R chose the precedence they did. One example that makes a fair amount of sense would be this one:

if (x == 1 & y == 0) {
    /* ... */
}

Since this is the bitwise AND operator, it uses a non-short-circuiting evaluation mode, as would

if (x == 1 | y == 0) {
    /* ... */
}

use the non-short-circuiting OR operator. This is probably why they chose to have the precedence group this way, but I agree with you that in retrospect it doesn't seem like a good idea.

Upvotes: 5

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