Typedef Union For Different Definitions Of The Same Memory Locations

typedef union _SYSTEM_CONFIGURATION_TYPEDEF
{
    DWORD dw[25];
    WORD w[50];
    BYTE b[100];
} SYSTEM_CONFIGURATION_TYPEDEF;

SYSTEM_CONFIGURATION_TYPEDEF system_config_buffer;

	system_config_buffer.b[0] = 1;
	system_config_buffer.b[1] = 2;
	system_config_buffer.b[2] = 3;
	system_config_buffer.b[3] = 4;
	system_config_buffer.b[4] = 5;
	//Will give:
	//system_config_buffer.w = 0x0201
	//system_config_buffer.dw = 0x04030201

Typedef Struct

typedef struct _TEST_HEADER
{
  WORD source_port;
  DWORD sequence_number;
  WORD window;
} TEST_HEADER;

Typedef Struct For A Buffer Of Different Registers In An Buffer

typedef struct _TEST_HEADER
{
	WORD source_port;
	DWORD sequence_number;

	union		//<<< You can also have unions inside a struct
	{
		struct
		{
			BYTE flag_fin	:1;
			BYTE flag_syn	:1;
			BYTE flag_rst	:1;
			BYTE flag_psh	:1;
			BYTE flag_ack	:1;
			BYTE flag_urg	:1;
			BYTE reserved	:2;
		} bits;
		BYTE byte;
	} flags;

	WORD window;
} TEST_HEADER;

A Union To Convert Float To Bytes And Bytes To Float

union FLOAT_BYTES
{
	float f;
	BYTE v[sizeof(float)];
};
//HOW TO USE:
//	FLOAT_BYTES my_value;
//	my_value.f = 0.1234;
//	BYTE x = my_value.v[0];

Handy Conversions

typedef union _MODBUS_ARRAY_TYPEDEF
{
    WORD w[(NV_MEMORY_LENGTH >> 1)];
    BYTE v[NV_MEMORY_LENGTH];
} MODBUS_ARRAY_TYPEDEF;

typedef union _FLOAT_BYTES
{
	float f;
	uint16_t w[2];
	uint8_t v[4];
}FLOAT_BYTES;
//HOW TO USE:
//	FLOAT_BYTES my_value;
//	my_value.f = 0.1234;
//	BYTE x = my_value.v[0];

typedef union _DOUBLE_BYTES
{
	double d;
	WORD w[2];
	BYTE v[4];
}DOUBLE_BYTES;

typedef union _SIGNED_WORD_BYTES
{
	SIGNED_WORD sw;
	WORD w;
	BYTE v[2];
}SIGNED_WORD_BYTES;

Union and Struct combined

#define	NV_MEMORY_LENGTH			20
typedef struct _NON_VOLATILE_STRUCT
{
	union
	{
		struct
		{
			uint32_t my_u32_val_1;
			uint32_t my_u32_val_2;
			uint16_t my_u16_val_1;
			//<<<Add others here
		} val;
		uint8_t b[NV_MEMORY_LENGTH];
	};
} NON_VOLATILE_STRUCT;
//non_volatile.val.
//non_volatile.b[]

NON_VOLATILE_STRUCT non_volatile;


	non_volatile.val.my_u32_val_1 = 0x12345678;
	non_volatile.b[0] = 0x12;