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There is info on this on the Wiki and previous message threads.
With VC6 if a C module throws an exception then the C++ does
no unwinding.

Note that if you are using VC6 you must compile with 


this allows C++ to believe that C functions might throw an 

Whatever compiler you are using - check the exception handling
options for mixed C and C++.

Given the above, auto_ptrs work fine.

David B

Francisco Socal <> wrote:

>Hi there,
>How can one be sure that locally allocated memory will be released when an error 
>occurs during the execution of some function of the Lua API? As in the following 
>code, per example: `foo` is never deleted as an error occurs and the execution 
>is tranfered back to `main`.
>    int pmain( lua_State* L )
>    {
>       Foo* foo = new Foo;
>       lua_pushstring( L, "This should be a table." );
>       lua_pushstring( L, "The next line will cause a run-time error." );
>       lua_gettable( L, -2 );
>       delete foo;
>       return 0;
>    }
>    int main()
>    {
>       lua_State* L = lua_open();
>       lua_cpcall( L, pmain, 0 );
>       lua_close(L);
>       return 0;
>    }
>Looking at the Lua exception handling mechanism, I noticed that it is possible 
>to redefine `L_THROW` and `L_TRY` via the `LUA_USEEXCEPTIONS` macro, so as to 
>use exceptions and let compiler generate the necessary cleanup code. This way, 
>one could safely wrap `foo` with something like `std::auto_ptr` and just don't 
>worry about memory management anynore.
>But I definitively don't want to change my Lua libraries and start using C++ to 
>build them. So I was wondering how could that be done purely in Lua, possibly 
>pushing `foo` somehow to the Lua stack as userdata and using its `__gc` 
>metamethod... Any idea?