Clever Geek Handbook

LuaJit FFI Returns a string from C to Lua function?

Let's 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 to get the returned string from a C function as a Lua string here:

local mymodule = require "mymodule"

print(mymodule.get_str())
+3


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1 answer


The function ffi.string

appears to be performing the conversion you are looking for.

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


If you get a crash, make sure your C string is null terminated and in your case has no more than 31 characters (so as not to overflow its buffer).

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