Convert an array to a binary string
BString_Type array_to_bstring (Array_Type a)
The array_to_bstring function returns the elements of an
array a as a binary string.
Convert a binary string to an array of bytes
UChar_Type[] bstring_to_array (BString_Type b)
The bstring_to_array function returns an array of unsigned
characters whose elements correspond to the bytes in the
binary string.
Concatenate binary strings
String_Type bstrcat (BString_Type a_1, ..., BString_Type a_N)
The bstrcat function concatenates its N binary string
arguments a_1, ... a_N together and returns the result.
This function will produce a result that is identical to that of
strcat if the input strings do not contain null characters.
Concatenate elements of an array of BString_Type objects
String_Type bstrjoin (Array_Type a [, BString_Type delim])
The bstrjoin function operates on an array of binary strings
by joining successive elements together separated with the optional
delimiter delim. If delim is not specified, then
empty string "" will be used resulting in a concatenation of
the elements.
Get the length of a binary string
UInt_Type bstrlen (BString_Type s)
The bstrlen function may be used to obtain the length of a
binary string. A binary string differs from an ordinary string (a C
string) in that a binary string may include null characters.
s = "hello\0";
len = bstrlen (s); % ==> len = 6
len = strlen (s); % ==> len = 5
Count the number of occurrences of a byte in a binary string
UInt_Type count_byte_occurrences (bstring, byte)
This function returns the number of times the specified byte
occurs in the binary string bstr.
This function uses byte-semantics. If character semantics are
desired, use the count_char_occurrences function.
test if a binary string contains a series of bytes
Int_Type is_substrbytes (a, b [,ofs])
This function may be used to see if the binary string a
contains the byte-sequence given by the binary string b. If
b is contained in a, then a ones-based offset of the
first occurance of b in a is returned. Otherwise, the
function will return 0 to indicate that a does not contain
b.
An optional 1-based parameter ofs may be passed to the function
to indicate where in a the search is to start. The returned
value is still a 1-based offset from the beginning of a where
b is located.
Support for the optional argument was added in version 2.3.0.
Pack objects into a binary string
BString_Type pack (String_Type fmt, ...)
The pack function combines zero or more objects (represented
by the ellipses above) into a binary string according to the format
string fmt.
The format string consists of one or more data-type specification characters defined by the following table:
c signed byte
C unsigned byte
h short
H unsigned short
i int
I unsigned int
l long
L unsigned long
m long long
M unsigned long long
j 16 bit int
J 16 bit unsigned int
k 32 bit int
K 32 bit unsigned int
q 64 bit int
Q 64 bit unsigned int
f float
d double
F 32 bit float
D 64 bit float
s character string, null padded
S character string, space padded
z character string, null padded
x a null pad character
s and S specifiers, the length
specifier indicates how many objects of that data type are to be
packed or unpacked from the string. When used with the s,
S, or z specifiers, it indicates the field width to be
used. If the length specifier is not present, the length defaults
to one.
When packing, unlike the s specifier, the z specifier
guarantees that at least one null byte will be written even if the
field has to be truncated to do so.
With the exception of c, C, s, S, and
x, each of these may be prefixed by a character that indicates
the byte-order of the object:
> big-endian order (network order)
< little-endian order
= native byte-order
When unpacking via the unpack function, if the length
specifier is greater than one, then an array of that length will be
returned. In addition, trailing whitespace and null characters are
stripped when unpacking an object given by the S specifier.
Trailing null characters will be stripped from an object represented
by the z specifier. No such stripping is performed by the s
specifier.
a = pack ("cc", 'A', 'B'); % ==> a = "AB";
a = pack ("c2", 'A', 'B'); % ==> a = "AB";
a = pack ("xxcxxc", 'A', 'B'); % ==> a = "\0\0A\0\0B";
a = pack ("h2", 'A', 'B'); % ==> a = "\0A\0B" or "\0B\0A"
a = pack (">h2", 'A', 'B'); % ==> a = "\0\xA\0\xB"
a = pack ("<h2", 'A', 'B'); % ==> a = "\0B\0A"
a = pack ("s4", "AB", "CD"); % ==> a = "AB\0\0"
a = pack ("s4s2", "AB", "CD"); % ==> a = "AB\0\0CD"
a = pack ("S4", "AB", "CD"); % ==> a = "AB "
a = pack ("S4S2", "AB", "CD"); % ==> a = "AB CD"
a = pack ("z4", "AB"); % ==> a = "AB\0\0"
a = pack ("s4", "ABCDEFG"); % ==> a = "ABCD"
a = pack ("z4", "ABCDEFG"); % ==> a = "ABC\0"
Add padding to a pack format
BString_Type pad_pack_format (String_Type fmt)
The pad_pack_format function may be used to add the
appropriate padding characters to the format fmt such that the
data types specified by the format will be properly aligned on word
boundaries. This is especially important when reading or writing files
that assume the native alignment.
Compute the size implied by a pack format string
UInt_Type sizeof_pack (String_Type fmt)
The sizeof_pack function returns the size of the binary string
represented by the format string fmt. This information may be
needed when reading a structure from a file.
Unpack Objects from a Binary String
(...) = unpack (String_Type fmt, BString_Type s)
The unpack function unpacks objects from a binary string
s according to the format fmt and returns the objects to
the stack in the order in which they were unpacked. See the
documentation of the pack function for details about the
format string.
(x,y) = unpack ("cc", "AB"); % ==> x = 'A', y = 'B'
x = unpack ("c2", "AB"); % ==> x = ['A', 'B']
x = unpack ("x<H", "\0\xAB\xCD"); % ==> x = 0xCDABuh
x = unpack ("xxs4", "a b c\0d e f"); % ==> x = "b c\0"
x = unpack ("xxS4", "a b c\0d e f"); % ==> x = "b c"