Just another Perl shrine | |
PerlMonks |
perlfunc:packby gods (Initiate) |
on Aug 24, 1999 at 22:42 UTC ( [id://220]=perlfunc: print w/replies, xml ) | Need Help?? |
packSee the current Perl documentation for pack. Here is our local, out-dated (pre-5.6) version: pack - convert a list into a binary representation
pack TEMPLATE,LIST
Takes an array or list of values and packs it into a binary structure, returning the string containing the structure. The TEMPLATE is a sequence of characters that give the order and type of values, as follows:
A An ascii string, will be space padded. a An ascii string, will be null padded. b A bit string (ascending bit order, like vec()). B A bit string (descending bit order). h A hex string (low nybble first). H A hex string (high nybble first).
c A signed char value. C An unsigned char value.
s A signed short value. S An unsigned short value. (This 'short' is _exactly_ 16 bits, which may differ from what a local C compiler calls 'short'.)
i A signed integer value. I An unsigned integer value. (This 'integer' is _at_least_ 32 bits wide. Its exact size depends on what a local C compiler calls 'int', and may even be larger than the 'long' described in the next item.)
l A signed long value. L An unsigned long value. (This 'long' is _exactly_ 32 bits, which may differ from what a local C compiler calls 'long'.)
n A short in "network" (big-endian) order. N A long in "network" (big-endian) order. v A short in "VAX" (little-endian) order. V A long in "VAX" (little-endian) order. (These 'shorts' and 'longs' are _exactly_ 16 bits and _exactly_ 32 bits, respectively.)
f A single-precision float in the native format. d A double-precision float in the native format.
p A pointer to a null-terminated string. P A pointer to a structure (fixed-length string).
u A uuencoded string.
w A BER compressed integer. Its bytes represent an unsigned integer in base 128, most significant digit first, with as few digits as possible. Bit eight (the high bit) is set on each byte except the last.
x A null byte. X Back up a byte. @ Null fill to absolute position.
Each letter may optionally be followed by a number giving a repeat count.
With all types except Examples:
$foo = pack("cccc",65,66,67,68); # foo eq "ABCD" $foo = pack("c4",65,66,67,68); # same thing
$foo = pack("ccxxcc",65,66,67,68); # foo eq "AB\0\0CD"
$foo = pack("s2",1,2); # "\1\0\2\0" on little-endian # "\0\1\0\2" on big-endian
$foo = pack("a4","abcd","x","y","z"); # "abcd"
$foo = pack("aaaa","abcd","x","y","z"); # "axyz"
$foo = pack("a14","abcdefg"); # "abcdefg\0\0\0\0\0\0\0"
$foo = pack("i9pl", gmtime); # a real struct tm (on my system anyway)
sub bintodec { unpack("N", pack("B32", substr("0" x 32 . shift, -32))); } The same template may generally also be used in the unpack function. |
|