Re: [Discuss-gnuradio] ANCI-C vs Gnuradio/C++ speeeed

[Ilia Mirkin]

Quoting al davis <address@hidden>:

> On Friday 12 May 2006 18:24, Ilia Mirkin wrote:
> > Also, when you do
> >
> > vector<int> x;
> > x[0] = 5;
> >
> > keep in mind that internally it instantiates a new int
> > object, and then calls operator= on it. The compiler might
> > optimize this to a certain extent, but certainly not to the
> > level of simplicity of a single memory access/write.
>
> A good compiler will optimize it that well.
>
> Your code is wrong.  The vector x is of size zero.  It should
> crash.
>
> You need:
> vector<int> x;
> x.reserve(5);
> x[0] = 5;
>
> or:
> vector<int> x(5);
> x[0] = 5;

OK, I suppose I was just giving an *idea* of what I was comparing rather than
fully working compiled code. But you're right -- I just checked the generated
code, and the only difference came from the array being on the stack vs
somewhere on the heap, which is to be expected. I hadn't realized that
compilers had come this far in terms of STL optimization.

 -Ilia