c

How to use LuaJIT's ffi module when embedding?

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I'm trying to embed LuaJIT into a C application. The code is like this: #include <lua.h> #include <lualib.h> #include <lauxlib.h> #include <stdlib.h> #include <stdio.h> int barfunc(int foo) { /* a dummy function to test with FFI */ return foo + 1; } int main(void) { int status, result; lua_State *L; L = luaL_newstate(); luaL_openlibs(L); /* Load the file containing the script we are going to run */ status = luaL_loadfile(L, "hello.lua"); if (status) { fprintf(stderr, "Couldn't load file: %s\n", lua_tostring(L, -1)); exit(1); } /* Ask Lua to run our little script */ result = lua_pcall(L, 0, LUA_MULTRET, 0); if (result) { fprintf(stderr, "Failed to run script: %s\n", lua_tostring(L, -1)); exit(1); } lua_close(L); /* Cya, Lua */ return 0; } the Lua code is like this: -- Test FFI local ffi = require("ffi") ffi.cdef[[ int barfunc(int foo); ]] local barreturn = ffi.C.barfunc(253) io.write(barreturn) io.write('\n') It reports error like this: Failed to run script: hello.lua:6: cannot resolve symbol 'barfunc'. I've searched around and found that there're really little document on the ffi module. Thanks a lot. c lua ffi luajit share|improve this question asked May 7 '11 at 7:37 jagttt 4541518

1   There's some docs here /ext_ffi.html - hth –  daven11 May 7 '11 at 7:55 Well I've checked that and it didn't cover my problem :( –  jagttt May 7 '11 at 9:10 You'll probably do way better posting this on the lua mailing list, which Mike Pall actively monitors, and will probably post an answer –  Necrolis May 7 '11 at 9:46 If you get an answer from the mailing list it wouldn't hurt to post it here too (where it is more likely to be found with a Google search.) –  finnw May 7 '11 at 10:35 add comment

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up vote 8 down vote accepted

ffi library requires luajit, so you must run lua code with luajit. From the doc: "The FFI library is tightly integrated into LuaJIT (it's not available as a separate module)". How to embed luajit? Look here http:///install.html under "Embedding LuaJIT" Under mingw your example run if i add __declspec(dllexport) int barfunc(int foo) at the barfunc function. Under Windows luajit is linked as a dll. share|improve this answer edited May 7 '11 at 17:12 answered May 7 '11 at 12:33 misianne 1405

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up vote 2 down vote

As misianne pointed out, you need to export the function, which you can do by using extern if you are using GCC: extern "C" int barfunc(int foo) { /* a dummy function to test with FFI */ return foo + 1; } If you are experiencing problems with undefined symbols under Linux using GCC, take care to have the linker add all symbols to the dynamic symbol table, by passing the -rdynamic flag to GCC: g++ -o application soure.cpp -rdynamic -I... -L... -llua share|improve this answer edited Apr 22 '12 at 20:10 answered Apr 22 '12 at 19:20 Martin K?llman 584314

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For those of you trying to make this work on Windows with VC++ (2012 or later), using the C++ compiler: make sure you use the .cpp extension, as this will do C++ compilation make the function have external C linkage so that ffi can link to it, with extern "C" { ... } export the function from the executable, with __declspec(dllexport) optionally specify the calling convention __cdecl, not required because should be it by default and not portable wrap the Lua headers in an extern "C" { include headers }, or better just #include "lua.hpp" #include "lua.hpp" extern "C" { __declspec(dllexport) int __cdecl barfunc(int foo) { return foo + 1;