serialize

• Index

Contents

• Functions

Modules

• lpack
• marshal
• struct

Module struct

Corona binding to struct, a library offering basic facilities to convert Lua values to and from C structs.

local struct = require("plugin.serialize").struct

Its main functions are pack, which packs multiple Lua values into a struct-like string; and 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). You can change these settings with appropriate directives in the format string.

The elements in the format string are as follows:

• " " (empty space) ignored.
• "!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.
• "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).
• "T" a size_t (native size).
• "in" a signed integer with n bytes. 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.

Notice in the original:

This package is distributed under the MIT license. See copyright notice at the end of file struct.c.

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];
  };
  

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 can 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)

Note 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
    a[#a + 1] = d
  end
  

• To pack a string in a fixed-width field of 10 characters padded with blanks, do as follows:

  x = struct.pack("c10", s .. string.rep(" ", 10))
  

Functions

pack (fmt, ...)	Returns a string containing the values packed according to the format string fmt.
unpack (fmt, s[, i=1])	Returns the values packed in string s according to the format string fmt.
size (fmt)	Returns the size of a string formatted according to the format string fmt.

Functions

pack (fmt, ...)

Returns a string containing the values packed according to the format string fmt.

Parameters:

• fmt string Format string.
• ... Values to pack.

Returns:

string Packed string.

unpack (fmt, s[, i=1])

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.

Parameters:

• fmt string Format string.
• s string String to unpack.
• i int Initial read position. (default 1)

Returns:

1. One or more values unpacked from string.
2. int Next position to read.

size (fmt)

Returns the size of a string formatted according to the format string fmt. The format string should contain neither the option "s" nor the option "c0".

Parameters:

• fmt string Format string

Returns:

uint Size.