Separator to make binary literals look cleaner

Question

I am trying to write binary literals in a cleaner format.

I understand that the following can be done for integer literals:

int x = 1234_5678_9999;

I assumed this would work for binary literals, so I tried:

uint32_t branch_bitmask = 0b0000_1111_0000_0000_0000_0000_0000_0000;

Which gives me an "invalid suffix" error for everything past the first underscore.

Is there an alternative to underscores that would allow me to write the binary literal in a cleaner way than just:

uint32_t branch_bitmask = 0b00001111000000000000000000000000;

Answer 1

If you always have the same number of bits (32 in your example) you could #define a macro a bit like this:

#define BITS32(b1,b2,b3,b4,b5,b6,b7,b8) ( \
  ((b1) << 28) + \
  ((b2) << 24) + \
  ((b3) << 20) + \
  ((b4) << 16) + \
  ((b5) << 12) + \
  ((b6) << 8) + \
  ((b7) << 4) + \
  (b8))

and then call it like this:

uint32_t branch_bitmask = BITS32(0b0000,0b1111,0b0000,0b0000,0b0000,0b0000,0b0000,0b0000);

or you can go further and use ## in the macro to prepend the 0b.

But the simple answer for me has always been to use hexadecimal, as one hex digit is 4 bits.

uint32_t branch_bitmask = 0x0F000000;