Is there a defined evaluation order for &= and |= ?

Question

If you have a C function which returns an integer, you could write a statement like this:

MyInt &= MyFunc();

...where we're using the bitwise-AND assignment operator.

The question is: is MyFunc() guaranteed to be executed, even if MyInt equals zero?

Likwise, if we used the bitwise-OR assignment operator (|=), would MyFunc() always be executed, even if MyInt were set to all ones?

Put another way: is lazy evaluation permitted in C for bitwise operators?

Answer 1

No. Bitwise operators are not short-circuited. MyFunc() execution is guaranteed regardless of the value of MyInt.

Answer 2

MyInt &= MyFunc();

is equivalent to:

MyInt = MyInt & MyFunc();

The language states that the & operator is not short-circuited. However, an optimiser could generate code not to call to the function if MyInt was zero and it was sure that the function had no side effects. I doubt any compilers acrtually do this, as the runtime test probably makes it a pessimisation.