http://www.inf.puc-rio.br/~roberto/struct/
teststruct? ?http://www.inf.puc-rio.br/~roberto/struct/teststruct
经过测试,可以直接编译进官方lua 与 luajit内
Library for Converting Data to and from C Structs for Lua 5.1
(download)
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:
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"!n"?flag to set the current alignment requirement to?n?(necessarily a power of 2); an absent?n?means the machine's native alignment.
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">"?flag to set mode to big endian.
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"<"?flag to set mode to little endian.
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" "?(empty space) ignored.
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"x"?a padding zero byte with no corresponding Lua value.
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"b"?a signed?char.
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"B"?an unsigned?char.
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"h"?a signed?short?(native size).
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"H"?an unsigned?short?(native size).
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"l"?a signed?long?(native size).
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"L"?an unsigned?long?(native size).
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"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.
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"In"?like?"in"?but unsigned.
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"f"?a?float?(native size).
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"d"?a?double?(native size).
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"s"?a zero-terminated string.
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"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).
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"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
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The code?print(struct.size("i"))?prints the size of a machine's native?int.
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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".
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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).
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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.
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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",i)
if d == 0 then break end
table.insert(a,d)
end
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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 $
