464b92e4   
   From: daniel.kruegler@googlemail.com   
      
   On 2012-02-29 12:58, Kris Prad wrote:   
   > This code snippet results in compiler warning:   
   >   
   > ----   
   > #include   
   > class A; // fwd class decl.   
   >   
   > void test()   
   > {   
   >       A* a;   
   >       std::auto_ptr  ap(a); // A is not defined here   
   > }   
      
   This code is non-conforming. std::auto_ptr requires (implied by the   
   general library requirements) that the template argument must be a   
   complete type.   
      
   > On Comeau online compiler:   
   > "memory", line 76: warning: delete of pointer to incomplete class   
   >       ~auto_ptr() { delete _M_ptr; }   
   >   
   > My question:   
   > Eventually ~auto_ptr() must see the underlying class definition for   
   > the code to work correctly. So, why is this only a warning, and not a   
   > full fledged error?   
      
   Note that there is no fundamental need for a constructor to see the   
   complete type. The language explicitly describes when this is   
   well-defined (The short version is: If the type has a non-trivial   
   destructor or a class-specific deallocation function).   
      
   If you can, use std::unique_ptr (from C++1): It is specified to make the   
   code ill-formed (including diagnostic), if the template parameter is   
   incomplete, when std::unique_ptr's destructor is instantiated.   
      
   HTH & Greetings from Bremen,   
      
   Daniel Krügler   
      
      
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