Re: [luabind] catching a luabind::error and getting info from it

[Arvid N. <c9...@cs...>]

Kevin Watters wrote:
> I'm running into problems getting good error information from 
> luabind::error exceptions that get thrown when there are errors in Lua 
> functions I call from C++ code.  If you just use e.what() all you get is 
> "lua runtime error," which isn't quite descriptive enough for my needs, 
> I'm not a perfect programmer :) I understand that the error can't 
> actually contain the message because of all the exceptions throwing 
> exceptions thing. But here's a code snippet:
> 
> try {
>    call_member<void>(self,"process",nowTime);
> } catch ( const luabind::error& e ) {
>    const char* message = lua_tostring(e.state(), -1);
>    panicMessageBox(message);
> }
> 
> I did some searching on the mailing list and found a post related to 
> this same problem. The reply was:
> 
> The reason we don't pass the actual message through the exception is 
> that we want to avoid heap allocations in our exception classes. Because 
> if that heap allocation would fail (i.e. if the exception class throws 
> another exception) the application would be terminated.
> 
> The message is passed on the stack, you could do something like this:
> 
> try
> {
>         luabind::call_function<void>(L, "Foo");
> }
> catch (const luabind::error& e)
> {
>         const char* message = lua_tostring(e.state(), -1);
>         std::cout << message << "\n";
> }
> 
> Which is exactly what I'm doing, but an "unhandled exception" still gets 
> thrown on the lua_tostring. Here's what the stack looks like in vs.net 
> when it crashes:
> 
>  >    msvcr71d.dll!strlen()  Line 78    Asm
>     msvcp71d.dll!std::char_traits<char>::length(const char * 
> _First=0x00000000)  Line 442 + 0x9    C++
>     
> msvcp71d.dll!std::basic_string<char,std::char_traits<char>,std::allocator<char> 
>  >::assign(const char * _Ptr=0x00000000)  Line 622 + 0x9    C++
>     
> msvcp71d.dll!std::basic_string<char,std::char_traits<char>,std::allocator<char> 
>  >::basic_string<char,std::char_traits<char>,std::allocator<char> 
>  >(const char * _Ptr=0x00000000)  Line 363    C++
>     tileDEBUG.exe!Object_wrapper::process(unsigned int nowTime=32)  Line 
> 116 + 0x17    C++
> 
> So I'm not quite sure what's happening. The docs say not to access the 
> lua state after it has been destructed, but I don't see why it would 
> have been destructed before the catch. Any suggestions?
> 
> -Kevin

That callstack doesn't seem to point into any lua nor luabind code. Are
you successfully catching the luabind exception?

One thing you could try is to make sure e.state() == self, they should
be.

-- 
Arvid Norberg