Re: [boost] Re: in/out parameters, codingstylesandmaintenance

From: Noel Yap (Noel.Yap_at_[hidden])
Date: 2003-05-03 23:25:11

Terje Slettebø wrote:
> 
> >From: "Justin M. Lewis" <boost_at_[hidden]>
> > void MyGetCWD(c_out<std::string> cwd)
> > {
> >     char *buf = new char[FIRSTSIZE];
> >     unsigned int size = FIRSTSIZE;
> >     while(getcwd(buf, sizeof(buf)) == NULL)
> >     {
> >         delete [] buf;
> >         size += step;
> >         buf = new char[size];
> >     }
> >
> >     cwd = buf;
> >     delete[] buf;
> > }
> 
> std::string MyGetCWD()
> {
>   // ...
> 
>   return std::string(buf);
> }
> 
> With a compiler implementing the Return Value Optimisation, which is a
> common optimisation, this is just as efficient as the example above, and
> requires no out parameter. It seems you're doing premature optimisation in
> this case.

I think your version may actually be faster than the version with
c_out<>.  For example:

  std::string cwd; // memory allocation here
  MyGetCWD( c_in_out( cwd ) ); // possible memory reallocation here

may perform more memory allocation/deallocation than:

  std::string cwd( MyGetCWD() ); // with RVO, only one memory allocation
(for std::string) AFAICT

Noel