I have a file I opened as binary like this: local dem = io.open("testdem.dem", "rb")
I can read out strings from it just fine: print(dem:read(8)) -> HL2DEMO, however, afterwards there is a 4-byte little endian integer and a 4-byte float (docs for the file format don't specify endianess but since it didn't specify little like the integer I'll have to assume big).
This cannot be read out with read.
I am new to the LuaJIT FFI and am not sure how to read this out. Frankly, I find the documentation on this specific aspect of the FFI to be underwhelming, although I'm just a lua programmer and don't have much experience with C. One thing I have tried is creating a cdata, but I don't think I understand that:
local dem = io.open("testdem.dem", "rb")
print(dem:read(8))
local cd = ffi.new("int", 4)
ffi.copy(cd, dem:read(4), 4)
print(tostring(cd))
--[[Output
HL2DEMO
luajit: bad argument #1 to 'copy' (cannot convert 'int' to 'void *')
]]--
Summary:
Goal: Read integers and floats from binary data.
Expected output: A lua integer or float I can then convert to string.
string.unpack does this for Lua 5.3, but there are some alternatives for LuaJIT as well. For example, see this answer (and other answers to the same question).