Integer constants can be written as binary constants, consisting of a sequence of ‘0’ and ‘1’ digits, prefixed by ‘0b’ or ‘0B’. This is particularly useful in environments that operate a lot on the bit level (like microcontrollers).
The following statements are identical:
i = 42; i = 0x2a; i = 052; i = 0b101010;
The type of these constants follows the same rules as for octal or hexadecimal integer constants, so suffixes like ‘L’ or ‘UL’ can be applied.
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https://gcc.gnu.org/onlinedocs/gcc-7.3.0/gcc/Binary-constants.html