gcc union bit field example

// gcc -Wall -o union union.c

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

typedef struct test
{
	union
	{
		uint8_t reg8bit;	// overall register
		struct
		{
			uint8_t bit05:6;	// bits 0-5
			uint8_t bit68:3;	// bits 6-8 .. ooops, too large
		} regs;
	} REG0;

	union
	{
		uint8_t reg8bit;	// overall register
		struct
		{
			uint8_t bit05:6;	// bits 0-5
			uint8_t bit68:3;	// bits 6-8 .. ooops, too large
		} regs;
	} REG1;
} test_t;


int main(void)
{
	test_t * t = (test_t*)malloc(20);
	printf("sizeof(test_t): %d\n", sizeof(test_t));

	printf("t: 0x%p\n", t);
	printf("reg0: 0x%p\n", &t->REG0);
	printf("reg1: 0x%p\n", &t->REG1);
	printf("sizeof(t): %d\n", sizeof(t));


	return 0;
}