http://www.inf./~roberto/struct/
teststruct http://www.inf./~roberto/struct/teststruct
經(jīng)過(guò)測(cè)試,可以直接編譯進(jìn)官方lua 與 luajit內(nèi)
Library for Converting Data to and from C Structs for Lua 5.1
This library offers basic facilities to convert Lua values to and from C structs. Its main functions are struct.pack, which packs multiple
Lua values into a struct-like string; and struct.unpack, which unpacks multiple Lua values from a given struct-like string.
The fist argument to both functions is a format string, which describes the layout of the structure. The format string is a sequence of conversion elements, which respect the current endianess and the current
alignment requirements. Initially, the current endianess is the machine's native endianness and the current alignment requirement is 1 (meaning no alignment at all). We can change these settings with appropriate directives in the format string.
The elements in the format string are as follows:
"!n" flag to set the current alignment requirement to n (necessarily a power of 2); an absent n means the machine's native alignment.">" flag to set mode to big endian."<" flag to set mode to little endian." " (empty space) ignored."x" a padding zero byte with no corresponding Lua value."b" a signed char."B" an unsigned char."h" a signed short (native size)."H" an unsigned short (native size)."l" a signed long (native size)."L" an unsigned long (native size)."in" a signed integer with n bytes (where n must be a power of 2). An absent n means the native size of an int."In" like "in" but unsigned."f" a float (native size)."d" a double (native size)."s" a zero-terminated string."cn" a sequence of exactly n chars corresponding to a single Lua string. An absent n means 1. When packing, the given string must have at least n characters (extra characters are discarded)."c0" this is like "cn", except that the n is given by other means: When packing, n is the length of the given string; when unpacking, n is the value of the previous unpacked value (which must
be a number). In that case, this previous value is not returned.
Lua API
All functions are registered inside a table struct. ul>
struct.pack (fmt, d1, d2, ...)
Returns a string containing the values d1, d2, etc. packed according to the format string fmt.
struct.unpack (fmt, s, [i])
Returns the values packed in string s according to the format string fmt. An optional i marks where in s to start reading (default is 1). After the read values, this function also returns the index in s where
it stopped reading, which is also where you should start to read the rest of the string.
struct.size (fmt)
Returns the size of a string formatted according to the format string fmt. For obvious reasons, the format string cannot contain neither the option s nor the optionc0.
Installing
To install, simply compile the file struct.c as a dynamic library. In Linux you can use the following command:
> gcc -Wall -O2 -shared -o struct.so struct.c
In Mac, you should define the environment variable MACOSX_DEPLOYMENT_TARGET as 10.3 and then write
> gcc -bundle -undefined dynamic_lookup -Wall -O2 -o struct.so struct.c
In Windows, you must generate a DLL exporting the single symbol luaopen_struct.
Examples
-
The code print(struct.size("i")) prints the size of a machine's native int.
-
To pack and unpack the structure
struct Str {
char b;
int i[4];
};
in Linux/gcc/Pentium (little-endian, maximum alignment of 4), you can use the string "<!4biiii". -
If you need to code a structure with a large array, you may use string.rep to automatically generate part of the string format. For instance, for the structure
struct Str {
double x;
int i[400];
};
you may build the format string with the code "d"..string.rep("i", 400). -
To pack a string with its length coded in its first byte, use the following code:
x = struct.pack("Bc0", string.len(s), s)
To unpack that string, do as follows:
s = struct.unpack("Bc0", x)
Notice that the length (read by the element "B") is not returned. -
Suppose we have to decode a string s with an unknown number of doubles; the end is marked by a zero value. We can use the following code:
local a = {}
local i = 1 -- index where to read
while true do
local d
d, i = struct.unpack("d", s, i)
if d == 0 then break end
table.insert(a, d)
end
-
To pack a string in a fixed-width field with 10 characters padded with blanks, do as follows:
x = struct.pack("c10", s .. string.rep(" ", 10))
Tests
File teststruct contains a full test script for this package. It is also a good source of examples.
License
This package is distributed under the MIT license. See copyright notice at the end of file struct.c.
$Id: struct.html,v 1.4 2008/04/18 20:10:24 roberto Exp $
