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

Question

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 ?

Answer 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

Answer 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]);
   ...