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1: File Binary

Read and parse, or write bytes

There are 10 types of people: those who use binary arithmetic and those who don’t.

Read Binary

x 1: y     1:[x;y]

Where

  • x is a 2-item list (a string of types and an int vector of widths) of which the order determines whether the data is parsed as little-endian or big-endian
  • y is a file descriptor or string, or byte sequence

returns the content of y as a matrix.

q)(enlist 4;enlist"i")1:0x01000000                  / big endian
16777216
q)(enlist"i";enlist 4)1:0x01000000                  / little endian
1
q)show pi:(enlist"f";enlist 8)1:0x7fbdc282fb210940  / pi as little endian 64-bit float
3.141593
q).Q.s1 pi                                          / 1×1 matrix
",,3.141593"

Read two records containing an integer, a character and a short from a byte sequence. Note the integer is read with a 4-byte width, the character with 1 byte and the short with 2 bytes. (When reading byte sequences, recall that a byte is 2 hex digits.)

q)("ich";4 1 2)1:0x00000000410000FF00000042FFFF
0 255
A B
0 -1

q)("ich";4 1 2)1:"arthur!"
1752461921
u
8562

With offset and length:

/load 500000 records, 100000 at a time
q)d:raze{("ii";4 4)1:(`:/tmp/data;x;100000)}each 100000*til 5

Column types and widths

b        boolean         1
g        guid            16
x        byte            1
h        short           2
i        int             4
j        long            8
e        real            4
f        float           8
c        char            1
s        symbol          n
p        timestamp       8
m        month           4
d        date            4
z        datetime        8
n        timespan        8
u        minute          4
v        second          4
t        time            4
(blank)  skip

Q for Mortals §11.5.1 Fixed-Width Records

Save Binary

filesymbol 1: bytes     1:[filesymbol;bytes]

writes bytes to filesymbol and returns it. If filesymbol

  • does not exist, it is created, with any required directories
  • exists, it is overwritten
q)`:hello 1: 0x68656c6c6f776f726c64
`:hello

0: File Text
File system

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