expand-bytes()

“Decompose a byte sequence and store it into variables”

Decompose a byte sequence and store it into variables.

const uint8_t* expand_bytes(
        const uint8_t* b, const uint8_t* e, ...)

expand_bytes() takes a combination of iterators of type uint8_t* as parameters. These specify the beginning of the target to be parsed and the iterator just past the end. If parsing reaches the position of e, it results in an error and returns nullptr.

If there is no error in expansion, it returns the iterator for the next reading.

The variable parameters should be specified as follows:

Number of bytes	Data length	Explanation
`uint8_t`	1
`uint16_t`	2	Expanded as big-endian order
`uint32_t`	4	Expanded as big-endian order
`uint8_t[N]`	N	Fixed-length array of `uint8_t`
`std::pair<char*,N>`	N	A pair of array and array length N of type `char` or `uint8_t` created by `make_pair()`

Example

auto&& rx = the_twelite.receiver.read();

char fourchars[5]{};
auto&& np =
	expand_bytes(rx.get_payload().begin(), rx.get_payload().end()
		, make_pair((uint8_t*)fourchars, 4)
    );

// read rest of payload
uint8_t u8DI_BM_remote = 0xff;
uint16_t au16AI_remote[5];
expand_bytes(np, rx.get_payload().end()
	, u8DI_BM_remote
	, au16AI_remote[0]
	, au16AI_remote[1]
	, au16AI_remote[2]
	, au16AI_remote[3]
	, au16AI_remote[4]
);

In this example, first a 4-byte string is read. Here, make_pair() is used to explicitly read 4 bytes of data.

Using the returned iterator np as a base, the next data is read. The next data consists of a uint8_t type followed by five uint16_t types.

Background

To simplify the description of byte arrays of type uint8_t used for generating and extracting data payloads of wireless packets.

auto&& rx = the_twelite.receiver.read();
char fourchars[5]{};
uint8_t u8DI_BM_remote = 0xff;
uint16_t au16AI_remote[5];

uint8_t *p = rx.get_payload().begin();
fourchars[0] = p[0];
fourchars[1] = p[1];
fourchars[2] = p[2];
fourchars[3] = p[3];
fourchars[4] = 0;
p += 4;

u8DI_BM_remote = (p[0] << 8) + p[1]; p+=2;
au16AI_remote[0] = (p[0] << 8) + p[1]; p+=2;
...

The above is the simplest description, but you can read from byte arrays using Byte array utils as follows:

auto&& rx = the_twelite.receiver.read();
char fourchars[5]{};
uint8_t u8DI_BM_remote = 0xff;
uint16_t au16AI_remote[5];

uint8_t *p = rx.get_payload().begin();
fourchars[0] = G_BYTE(p);
fourchars[1] = G_BYTE(p);
fourchars[2] = G_BYTE(p);
fourchars[3] = G_BYTE(p);
fourchars[4] = 0;

u8DI_BM_remote = G_WORD(p);
au16AI_remote[0] = G_WORD(p);
...