Demonstrate bitfields

demo_bitfields.c

#include <inttypes.h>
#include <stdbool.h>
#include <stdio.h>

#define EPOLLIN  1
#define EPOLLOUT 4

struct simple
{
	bool read;
	bool write;
};

struct bitfields
{
	bool read : 1;
	bool write : 1;
};

struct adhoc
{
	bool read : 1;
	bool _ : 1;
	bool write : 1;
};

#define EVAL(expr)    #expr, expr
#define EVAL_PP(expr) #expr, EVAL(expr)

int main()
{
	printf("%-30s: %zu\n", EVAL(sizeof(struct simple)));
	printf("%-30s: %zu\n", EVAL(sizeof(struct bitfields)));
	printf("%-30s: %zu\n", EVAL(sizeof(struct adhoc)));

	struct adhoc read_and_write = {.read = true, .write = true};

	printf("%-22s= %s = %" PRIu8 "\n", EVAL_PP(EPOLLIN | EPOLLOUT));
	printf("%-30s= %" PRIu8 "\n", EVAL(read_and_write));
}

$ make demo_bitfields && ./demo_bitfields 
cc     demo_bitfields.c   -o demo_bitfields
sizeof(struct simple)         : 2
sizeof(struct bitfields)      : 1
sizeof(struct adhoc)          : 1
EPOLLIN | EPOLLOUT    = 1 | 4 = 5
read_and_write                = 5