Pack given arguments into binary string according to format. Returns binary string
containing data.
The idea to this function was taken from Perl and all
formatting codes work the same as there, however, there are
some formatting codes that are missing such as Perl's "u"
format code. The format string consists of format codes
followed by an optional repeater argument. The repeater
argument can be either an integer value or * for repeating to
the end of the input data. For a, A, h, H the repeat count
specifies how many characters of one data argument are taken,
for @ it is the absolute position where to put the next data,
for everything else the repeat count specifies how many data
arguments are consumed and packed into the resulting binary
string. Currently implemented are
h Hex string, low nibble first
H Hex string, high nibble first
s signed short (always 16 bit, machine byte
order)
S unsigned short (always 16 bit, machine byte
order)
n unsigned short (always 16 bit, big endian byte
order)
v unsigned short (always 16 bit, little endian byte
order)
i signed integer (machine dependent size and byte
order)
I unsigned integer (machine dependent size and byte
order)
l signed long (always 32 bit, machine byte
order)
L unsigned long (always 32 bit, machine byte
order)
N unsigned long (always 32 bit, big endian byte
order)
V unsigned long (always 32 bit, little endian byte
order)
f float (machine dependent size and
representation)
d double (machine dependent size and
representation)
Note that the distinction between signed and unsigned
values only affects the function unpack(),
where as function pack() gives the
same result for signed and unsigned format codes.
Also note that PHP internally stores integer
values as signed values of a machine dependent size. If you
give it an unsigned integer value too large to be stored that
way it is converted to a
float which often yields an undesired
result.