C++ bitfield packing with bools

Question

I\'ve just done a test with bitfields, and the results are surprising me.

class test1 {
public:
    bool test_a:1;
    bool test_b:1;
    bool test_c:1;
            


        

Answer 1

Be careful with bitfields as much of its behavior is implementation (compiler) defined:

From C++03, 9.6 Bitfields (pg. 163):

Allocation of bit-fields within a class object is implementation-defined. Alignment of bit-fields is implementation-defined. Bit-fields are packed into some addressable allocation unit. [Note:bit-fields straddle allocation units on some machines and not on others. Bit-fields are assigned right-to-left on some machines, left-to-right on others. ]

That is, it is not a bug in the compiler but rather lack of a standard definition of how it should behave.