lPack Documentation

• License
• Support
• Introduction
• Functions
  • string.pack
  • string.unpack
• Letter Codes

License

This code is hereby placed in the public domain.

Support

Please send comments, suggestions, and bug reports to lhf@tecgraf.puc-rio.br.

Introduction

This is a simple Lua library for packing and unpacking binary data.

The library adds two functions to the string library: pack and unpack.

Functions

string.pack

Prototype:

ret = pack( F, x1, x2, ... )

Description:

Packs binary data into a string.

Parameters:

F

A string describing how the values x1, x2, ... are to be interpreted and formatted. Each letter in the format string F consumes one of the given values. The letter codes understood by pack are listed below (they are inspired by Perl's codes but are not the same). Numbers following letter codes in F indicate repetitions.

x1, x2, ...

Values to pack into binary. Only values of type number or string are accepted.

Returns:

ret

A (binary) string containing the values packed as described in F.

string.unpack

Prototype:

val, next = unpack( s, F [,init] )

Description:

Packs binary data into a string.

Parameters:

s

A (binary) string containing data packed as if by pack.

F

A format string describing what is to be read from s

init

An optional init marks where in s to begin reading the values.

Returns:

next

The first value returned by unpack is the next unread position in s, which can be used as the init position in a subsequent call to unpack. This allows you to unpack values in a loop or in several steps. If the position returned by unpack is beyond the end of s, then s has been exhausted; any calls to unpack starting beyond the end of s will always return nil values.

val

One value per letter in F until F or s is exhausted (the letters codes are the same as for pack, except that numbers following A are interpreted as the number of characters to read into the string, not as repetitions).

Letter Codes

z : zero-terminated string
p : string preceded by length byte
P : string preceded by length word
a : string preceded by length size_t
A : string
f : float
d : double
n : Lua number
c : char
b : byte (unsigned char)
h : short
H : unsigned short
i : int
I : unsigned int
l : long
L : unsigned long

< : little endian
> : big endian
= : native endian