LuaJit FFI Return string from C function to Lua?

Question

Say I have this C function:

__declspec(dllexport) const char* GetStr()
{
    static char buff[32]

    // Fill the buffer with some string here

    return buff;
}

And this simple Lua module:

local mymodule = {}

local ffi = require("ffi")

ffi.cdef[[
    const char* GetStr();
]]

function mymodule.get_str()
    return ffi.C.GetStr()
end

return mymodule

How can I get the returned string from the C function as a Lua string here:

local mymodule = require "mymodule"

print(mymodule.get_str())

Answer 1

The ffi.string function apparently does the conversion you are looking for.

function mymodule.get_str()
    local c_str = ffi.C.GetStr()
    return ffi.string(c_str)
end

If you are getting a crash, then make sure that your C string is null terminated and, in your case, has at most 31 characterss (so as to not overflow its buffer).