OverviewOverview
This module allows for arbitrary packing of data into Lua strings and unpacking data from Lua strings. In this way, a string can be used to store data in a platform-indepdendent manner. It is based on the lpack module from Luiz Henrique de Figueiredo (with some minor tweaks).
Both methods of this module (pack and unpack) use a format string to describe how to pack/unpack the data. The format string contains one or more data specifiers, each data specifier is applied to a single variable that must be packed/unpacked. The data specifier has the following general format:
[endianness]<format specifier>[count]
where:
- endianness is an optional endian flags that specifies how the numbers that are to be packed/unpacked are stored in memory. It can be either:
- '<' for little endian.
- '>' for big endian.
- '=' for native endian (the platform's endian order, default).
- format specifier describes what kind of variable will be packed/unpacked. The format specifier is case-sensitive. The possible values of this parameter are summarized in the table below:
Format specifier Corresponding variable type '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 - count is an optional counter for the format specifier. For example, i5 instructs the code to pack/unpack 5 integer variables, as opposed to i that specifies a single integer variable.
Functions
packed = pack.pack( format, val1, val2, ..., valn )Packs variables in a string.
Arguments:
- format - format specifier (as described here).
- val1 - first variable to pack.
- val2 - second variable to pack.
- valn - nth variable to pack.
Returns: packed - a string containing the packed representation of all variables according to the format.
nextpos, val1, val2, ..., valn = pack.unpack( string, format, [ init ] )Unpacks a string
Arguments:
- string - the string to unpack.
- format - format specifier (as described here).
- init - (optional) marks where in string the unpacking should start (1 if not specified).
Returns:
- nextpos - the position in the string after unpacking.
- val1 - the first unpacked value.
- val2 - the second unpacked value.
- valn - the nth unpacked value.