pack

Syntax

pack(format, args…)

Details

Packs the data into a binary byte stream according to the format specified by format.

Parameters

format is a format string. See Appendix: Format Characters.

A format character may be preceded by an integral repeat count. For example, the format string 4h means exactly the same as hhhh.
Whitespace characters between formats are ignored; a count and its format must not contain whitespace though.
For the s format character, the count is interpreted as the length of the bytes, not a repeat count like for the other format characters; for example, 10s means a single 10-byte string, while 10c means 10 characters. If a count is not given, it defaults to 1. The string is truncated or padded with null bytes as appropriate to make it fit.

args... The data to be packed. The arguments must match the values required by the format exactly.

Returns

Returns a bytes object packed according to the format string format.

Examples

res = pack("N",1);
res1 = unpack("N", res);
print(res1)
// output: (1)

res = pack("iii", 1, 2, 3)
res1 = unpack("iii",  res);
print(res1)
// output: (1,2,3)

res = pack("x",NULL)
res = unpack("x",pack("x",NULL))
typestr(res[0])
// output: VOID

res = pack("3si", `123, 3)
res1 = unpack("3si",  res);
print(res1)
// output: ("123",3)

Related function: unpack

Appendix

Format Characters

Format mapping:


Format	C Type	Python Type	DolphinDB Type	Range
x	pad byte	no value	VOID
c	char	bytes of length 1	CHAR	-27 +1~27 -1
b	signed char	integer	LONG	-27 ~27 -1
B	unsigned char	integer	LONG	0~28 -1
?	_Bool	bool	LONG	-263 ~263 -1
h	short	integer	LONG	-215 ~215 -1
H	unsigned short	integer	LONG	0~216 -1
i	int	integer	LONG	-231 ~231 -1
I	unsigned int	integer	LONG	0~232 -1
l	long	integer	LONG	-231~231 -1
L	unsigned long	integer	LONG	0~232 -1
q	long long	integer	LONG	-263 ~263 -1
Q	unsigned long long	integer	LONG	0~263 -1
n	ssize_t	integer	LONG	-263 ~263 -1
N	size_t	integer	LONG	0~263 -1
f	float	float	LONG	-3.40E+38 ~ +3.40E+38
d	double	float	LONG	-1.79E+308 ~ +1.79E+308
s	char[]	bytes	STRING
p	char[]	bytes	STRING
P	void*	integer	LONG	-263 ~263 -1

Byte Order, Size, and Alignment


Character	Byte order	Size	Alignment
>	big-endian	standard	none
=	native	standard	none
<	little-endian	standard	none
@	native	native	native
!	network
(= big-endian)	native	none

The first character of the format string can be used to indicate the byte order, size and alignment of the packed data, see "Appendix: Byte Order, Size and Alignment". If the first character is not one of these characters, '@' is assumed.