What is the usage of the PHP unpack function?

The unpack function is used to unpack binary data into an array. Its basic usage is as follows:

array unpack ( string $format , string $data )

The $format parameter is a string used to specify the unpacking format, such as C representing an unsigned character, s representing a signed short integer, and so on. The $data parameter is the data to be unpacked.

For example, if you want to unpack a signed integer and an unsigned character into an array, you can do so like this:

$data = "\x04\x00\x00\x00\x41";
$result = unpack("Lint/Cchar", $data);

print_r($result);

The above code will produce:

Array
(
    [int] => 4
    [char] => 65
)

This achieves the function of unpacking binary data into an array.