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Possible values for the format parameter:
a-nul-padded string
a-space-padded string
H-hex string, low nibble-a
H-hex string, high nibble-a
c-signed Char
c-unsigned Char
s-signed short (always bit, machine byte)
s-unsigned short (always bit, machine byte)
n-unsigned short (always bit, big endian byte)
v-unsigned short (always bit, little endian byte)
i-signed integer (Machine dependent size and byte order)
i-unsigned integer (Machine dependent size and byte order)
L-signed long (always bit, machine byte order)
L-unsigned long (always bit, machine byte order)
N-unsigned long (always bit, big endian byte)
V-unsigned long (always 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 a filled-empty byte string
A a byte string filled with spaces
b A bit string, in which the order of bits in each byte is ascending
b A bit string, in which the order of the bits in each byte is descending
c A signed char (8-bit integer) value
c A unsigned char (8-bit integer) value; about Unicode see u
D-Native format double-precision floating-point number
F single-precision floating-point number in native format
h a hexadecimal string, low four bits in front
h a hexadecimal string, high four bits in front
I a signed integer value, native format
I a unsigned integer value, native format
L A signed long plastic, always 32-bit
L An unsigned long shaping, always 32-bit
N A 16-bit short shaping, "Network" byte order (big head in front)
N A 32-bit short shaping, "Network" byte order (big head in front)
p A pointer to a string that points to an empty end
p A pointer to a fixed-length string
Q A signed four times-fold (64-bit integer) value
Q A unsigned four times-fold (64-bit integer) value
s a signed short integer value, always 16 bits
s an unsigned short integer value, always 16 bits, and the byte sequence is related to the machine chip.
U a code-free string
U a Unicode character number
V A 16-bit short integer with a "VAX" byte order (front end)
V A 32-bit short integer with a "VAX" byte order (front end)
W A ber-compressed integer
X an empty byte (ignoring one byte forward)
X back up one byte
Z a null-terminated (and empty-filled) byte string
Rules:
1. Each letter can be followed by a number that represents count (count), if Count is a * represents the rest of the things.
2. If you provide fewer parameters than $format requirements, the pack assumes that the missing values are null. If you provide more arguments than $format, then the extra parameters are ignored.