These numeric operations effectively allow you to manipulate individual bits in variables, fitting since C is such a low-level langauge150.
If you’re not familiar with bitwise operations, Wikipedia has a good bitwise article151.
For each of these, the usual arithmetic conversions take place on the operands (which in this case must be an integer type), and then the appropriate bitwise operation is performed.
| Operation | Operator | Example |
|---|---|---|
| AND | & |
a = b & c |
| OR | | |
a = b | c |
| XOR | ^ |
a = b ^ c |
| NOT | ~ |
a = ~c |
Note how they’re similar to the Boolean operators && and ||.
These have assignment shorthand variants similar to += and -=:
| Operator | Example | Longhand equivalent |
|---|---|---|
&= |
a &= c |
a = a & c |
|= |
a |= c |
a = a | c |
^= |
a ^= c |
a = a ^ c |
For these, the integer promotions are performed on each operand (which must be an integer type) and then a bitwise shift is executed. The type of the result is the type of the promoted left operand.
New bits are filled with zeros, with a possible exception noted in the implementation-defined behavior, below.
| Operation | Operator | Example |
|---|---|---|
| Shift left | << |
a = b << c |
| Shift right | >> |
a = b >> c |
There’s also the same similar shorthand for shifting:
| Operator | Example | Longhand equivalent |
|---|---|---|
>>= |
a >>= c |
a = a >> c |
<<= |
a <<= c |
a = a << c |
Watch for undefined behavior: no negative shifts, and no shifts that are larger than the size of the promoted left operand.
Also watch for implementation-defined behavior: if you right-shift a negative number, the results are implementation-defined. (It’s perfectly fine to right-shift a signed int, just make sure it’s positive.)