util.string.packsize

Syntax

local size = util.string.packsize(
    format
)

Parameters

Type	Name	Description
`string`	format	Format string containing specifiers describing how to pack the values Refer Specifiers section

Returns

Type	Name	Description
`int`	size	The size in bytes of the packed string that would result from `util.string.pack`

Specifiers

Specifier	Description
`b`	Signed byte (char)
`B`	Unsigned byte (unsigned char)
`h`	Signed short
`H`	Unsigned short
`l`	Signed long
`L`	Unsigned long
`j`	lua_Integer
`J`	lua_Unsigned
`T`	size_t
`i[n]`	Signed int with n bytes
`I[n]`	Unsigned int with n bytes
`f`	Float
`d`	Double
`n`	Lua number
`c[n]`	Fixed-size string of n bytes
`z`	Zero-terminated string
`s[n]`	String preceded by length
`x`	One byte of padding
`<`	Set little endian
`>`	Set big endian
`=`	Set native endian

Examples

Get the size of three packed integers

local size = util.string.packsize("iii")

core.engine.print("info", size) -- 12

Get the size of a packed double

local size = util.string.packsize("d")

core.engine.print("info", size) -- 8

Get the size of a fixed-length string

local size = util.string.packsize("c10")

core.engine.print("info", size) -- 10

Get the size of multiple packed types

local size = util.string.packsize("ifd")

core.engine.print("info", size) -- 16

Get the size with a little endian specifier

local size = util.string.packsize("<I4")

core.engine.print("info", size) -- 4

Get the size of a packed byte

local size = util.string.packsize("b")

core.engine.print("info", size) -- 1

Get the size of a packed short

local size = util.string.packsize("h")

core.engine.print("info", size) -- 2

Get the size of a packed long

local size = util.string.packsize("l")

core.engine.print("info", size) -- 8

Get the size of a format with padding

local size = util.string.packsize("ixxi")

core.engine.print("info", size) -- 12

Compare sizes of different integer widths

core.engine.print("info", "i4:", util.string.packsize("i4")) -- 4
core.engine.print("info", "i8:", util.string.packsize("i8")) -- 8

Calculate the buffer size needed for a format

local fmt = "i4i4f"
local bufferSize = util.string.packsize(fmt)

core.engine.print("info", "Need", bufferSize, "bytes") -- 'Need 12 bytes'

Get the size of multiple fixed strings

local size = util.string.packsize("c5c5c5")

core.engine.print("info", size) -- 15

Verify packsize matches the actual packed length

local fmt = "ifd"
local size = util.string.packsize(fmt)
local packed = util.string.pack(fmt, 1, 2.5, 3.14)

core.engine.print("info", #packed == size) -- true

Pre-calculate record size for file buffers

local recordFormat = "c32i4i4"
local recordSize = util.string.packsize(recordFormat)

core.engine.print("info", "Each record:", recordSize, "bytes")

Calculate a network protocol header size

local headerFormat = ">I2I2I4"
local headerSize = util.string.packsize(headerFormat)

core.engine.print("info", "Header size:", headerSize) -- 8

Syntax

Parameters

Returns

Specifiers

Examples

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