Reading binary data
fredrik at pythonware.com
Wed Nov 23 21:09:15 CET 2005
"David M" wrote:
> What are u_ini16_t and comp_t?
comp_t is explained in the file you posted:
> comp_t is a 16-bit "floating" point number with a 3-bit base 8
> exponent and a 13-bit fraction. See linux/kernel/acct.c for the
> specific encoding system used.
> typedef u_int16_t comp_t;
as the comment says, comp_t is a 16-bit value. you can read it in as
an integer, but you have to convert it to a floating point according to
the encoding mentioned above.
the typedef says that comp_t is stored as a u_int16_t, which means
that it's 16-bit value too. judging from the name, and the fields using
it, it's safe to assume that it's an unsigned 16-bit integer.
> And what about the enum section?
it just defines a bunch of symbolic values; AFORK is 1, ASU is 2, etc.
> AFORK = 0x01, /* Has executed fork, but no exec. */
> ASU = 0x02, /* Used super-user privileges. */
> ACORE = 0x08, /* Dumped core. */
> AXSIG = 0x10 /* Killed by a signal. */
at this point, you should be able to do a little experimentation. read in
a couple of bytes (64 bytes should be enough), print them out, and try
to see if you can match the bytes with the description above.
f = open(filename, "rb")
data = f.read(64)
# hex dump
# list of decimal byte values
print map(ord, data)
# struct test (keep adding type codes until you're sorted everything out)
format = "BHHHHHH"
print struct.unpack(format, struct.calcsize(format))
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