Character meanings of php pack and unpack

Possible values of the format parameter:
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
@-NUL-fill to absolute position
A is a Null Byte string.
A is A byte string filled with spaces.
B is a single-byte string in ascending order.
B is a single-byte string. the bits in each byte are sorted in descending order.
C is a signed char (8-digit integer) value.
C is an unsigned char (8-digit integer) value. For Unicode, see U
D. double-precision floating point number in local format
F single-precision floating point number in local format
H: A hexadecimal string with four lower digits in front
H: A hexadecimal string with four digits in front
I a signed integer in the local format
I an unsigned integer in the local format
L a signed long integer, always 32-bit
L an unsigned long integer, always 32-bit
N a 16-bit short integer, "network" in byte order (front of the big head)
N a 32-bit short integer, "network" in byte order (front of the big head)
P a pointer to a null string
P a pointer to a fixed-length string
Q: A signed value of four times (64-bit integer)
Q: an unsigned four times (64-bit integer) Value
S a signed short integer value, always 16 bits
S is an unsigned short integer value, which is always 16 bits. The byte order is related to the machine chip.
U a non-encoded string
U a Unicode Character number
Va 16-bit short integer in the byte order of "VAX" (before the Small Header)
Vone is a 32-bit short integer in the byte order of "VAX" (before the Small Header ).
W: an integer compressed by a BER
X is an empty byte (ignore one byte forward)
X back up one byte
Z: An empty ending (and an empty-filled) byte string
Rules:
1. Each letter can be followed by a number, indicating count. If count is a *, it indicates all the remaining items.
2. If you provide fewer parameters than $ format, pack assumes that all parameters are missing are null values. If you provide more parameters than $ format, extra parameters are ignored.