Re: Calling Lua from C - have I been doing it wrongly?
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- Subject: Re: Calling Lua from C - have I been doing it wrongly?
- From: Glenn Maynard <glenn@...>
- Date: 2006年10月14日 18:14:22 -0400
On Sun, Oct 15, 2006 at 08:02:20AM +1000, Nick Gammon wrote:
> int main (void)
> {
> lua_State * L = luaL_newstate ();
> luaL_openlibs (L);
> int error = luaL_loadbuffer(L, buff, strlen(buff), "line") ||
> lua_pcall(L, 0, 0, 0);
> return 0;
> } // end of main
> ---------------
>
> Isn't there a problem here? What if luaL_loadbuffer fails? For
> example, out of memory? We can simulate a failure with this example
> program, which in essence does what caused my application to crash
> recently:
Set the default error handler, using lua_atpanic. The default is to
print an error and exit(), which is probably not what you want.
> I am familiar with doing lua_pcall to run the code that I ultimately
> want to run in a safe way, but I usually did something like this:
>
> lua_getglobal (L, "somefunction"); --> get some function
> lua_pushstring (L, "blah blah"); --> push arguments to function
> lua_pcall (L, 1, 1, 0); --> call the function
> const char * p = lua_checkstring (L, -1); --> oops! this might fail
I'd do eg:
const char *p = lua_tostring( L, -1 );
if( p == NULL )
{
error("somefunction: returned %s, expected a string", ...); // use your error handling of choice
return -1;
}
I only use lua_checkstring and the like from within C bindings, and
other places which are inside a pcall.
> So really, the whole sequence above should be protected itself by
> another level of lua_pcall, like I described. Am I right?
You can do it that way, though I think I'd find that cumbersome. You can
also set a new panic function for the code block:
lua_CFunction old = lua_atpanic(L, ErrorHandler);
...
lua_atpanic(L, old);
(Remember that you have to longjmp out of a panic handler.)
--
Glenn Maynard