PHP pack() Function

The pack() function packs data into a binary string.

string pack ( string $format [, mixed $args [, mixed $... ]] )

Pack given arguments into a binary string according to format.

The idea for this function was taken from Perl and all formatting codes work the same as in Perl. However, there are some formatting codes that are missing such as Perl's "u" format code.

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.

Example -

The resulting binary string will be 6 bytes long and contain the byte sequence 0x12, 0x34, 0x78, 0x56, 0x41, 0x42.

ParameterDescription
formatRequired. Specifies the format to use when packing data.
Possible values:
  • a - NUL-padded string
  • A - SPACE-padded string
  • h - Hex string, low nibble first
  • H - Hex string, high nibble first
  • c - signed char
  • C - unsigned char
  • 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)
  • x - NUL byte
  • X - Back up one byte
  • Z - NUL-padded string
  • @ - NUL-fill to absolute position
    • args+Optional. Specifies one or more arguments to be packed

    Return Values

    Returns a binary string containing data.