Setting the global LUA_PATH variable from C++/C?

12,495

Solution 1

In C++:

int setLuaPath( lua_State* L, const char* path )
{
    lua_getglobal( L, "package" );
    lua_getfield( L, -1, "path" ); // get field "path" from table at top of stack (-1)
    std::string cur_path = lua_tostring( L, -1 ); // grab path string from top of stack
    cur_path.append( ";" ); // do your path magic here
    cur_path.append( path );
    lua_pop( L, 1 ); // get rid of the string on the stack we just pushed on line 5
    lua_pushstring( L, cur_path.c_str() ); // push the new one
    lua_setfield( L, -2, "path" ); // set the field "path" in table at -2 with value at top of stack
    lua_pop( L, 1 ); // get rid of package table from top of stack
    return 0; // all done!
}

I haven't tested or compiled it. I used: http://lua.org/pil and http://lua.org/manual/5.1

Solution 2

ObjC: Following from the other answer, here's what works for me. The appending of "/?.lua" is needed.

int setLuaPath( NSString* path )  
{
    lua_getglobal( L, "package" );
    lua_getfield( L, -1, "path" ); // get field "path" from table at top of stack (-1)
    NSString * cur_path = [NSString stringWithUTF8String:lua_tostring( L, -1 )]; // grab path string from top of stack
    cur_path = [cur_path stringByAppendingString:@";"]; // do your path magic here
    cur_path = [cur_path stringByAppendingString:path];
    cur_path = [cur_path stringByAppendingString:@"/?.lua"];
    lua_pop( L, 1 ); // get rid of the string on the stack we just pushed on line 5
    lua_pushstring( L, [cur_path UTF8String]); // push the new one
    lua_setfield( L, -2, "path" ); // set the field "path" in table at -2 with value at top of stack
    lua_pop( L, 1 ); // get rid of package table from top of stack
    return 0; // all done!
}

   ... add this code somewhere, near where you lua_open() for example

   // Set Lua's Package.path to where our Lua files can be found
   NSString *luaPath = [[NSBundle mainBundle] pathForResource:@"name of any one of my lua files" ofType:@"lua"];
   setLuaPath([luaPath stringByDeletingLastPathComponent]);
   ...

Solution 3

You can set the LUA_PATH and LUA_CPATH within c++ very easily by executing a couple lual_dostring functions.

luaL_dostring(L, "package.path = package.path .. ';?.lua'");
luaL_dostring(L, "package.cpath = package.cpath .. ';?.dll'");

These two line called after you have your lua_State (L here) and before your lual_loadfile() and lau_pcall() function calls will add to the currently set path and cpath. In this case I add to both an instruction to look local to the execution.

It took me hours to find this solution.. I hope it helps.

Solution 4

You can also change package.path in Lua before calling require.

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Goles
Author by

Goles

Software Craftsman. Extremely interested in Web Technologies and Mobile Game Development. Using the sweet Obj-C, the evil C++ and the elegant Lua. Have been using lot's of Ruby spices in the mix lately.

Updated on March 07, 2020

Comments

  • Goles
    Goles over 3 years

    I'm trying to set my global LUA_PATH variable directly from C/C++, I'm using Lua from my iPhone applications, so my path tends does change between applications ( each iPhone app has a separate folder in the device ).

    I know I could set the LUA_PATH by recompiling lua with a "fixed" path, but that's quite far from ideal.

    ( I'm trying to do this in order to be able to use require, from my .lua scripts.

    Could anyone help me out here ?

  • Puppy
    Puppy about 13 years
    I believe that they used to be forbidden but aren't any longer.
  • Kai
    Kai about 13 years
    @DeadMG2 Maybe i missed something. I think no one ever reads in detail the frequent changes and additions to the contract
  • lhf
    lhf about 13 years
    Or env LUA_PATH="foo" /path/to/executable.
  • SoapiestWaffles
    SoapiestWaffles almost 11 years
    This works flawlessly, thank you. Exactly what i was looking for.
  • Watusimoto
    Watusimoto about 10 years
    I don't think LUA_PATH is an environment variable.
  • Shayne
    Shayne over 5 years
    This isn't an answer to the question.
  • OLL
    OLL almost 3 years
    I tried this, but luaL_dostring returns and error. The message I get is attempt to index a nil value (global 'package')
  • OLL
    OLL almost 3 years
    Actually turns that I was getting that error because I wasn't calling luaL_openlibs(L). This solution works if the package lib is loaded properly

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