[LC++]can't seem to use reference

[Carlo Wood]

On Tue, Feb 19, 2002 at 11:32:05AM +1030, Mark Phillips wrote:
> >   largeStructTy const& ls(largeStructList[i]);
> >   largeStructTy const& nextLs(largeStructList[i]);
> >   nextLs = largeStructList[i + 1];

> any case, both out pieces of code fail because C++ doesn't allow
> the reassignment of a reference.

Excuse me, but I am not reassigning a reference, the line
"nextLs = largeStructList[i + 1]" is doing the copying
that I thought were doing.  Thats what you get when you
write illegal code (nonsense thus).

> I am considering largeStructList to be a read-only array of
> large structures.  At each stage in the for loop I want to
> process things involving consecutive pairs.  I could, as you
> say, explicitly instantiate references to the two consecutive
> objects at each iteration.  But a better way would be to use
> the second reference at iteration i, as the first reference
> at iteration i+1, meaning there is no need to recalculate 
> it.  Unfortunately C++ syntax does not allow this.

Well, now I know what you want...

largeStructTy const* lsp = &largeStructList[0];			// Single, one time assembly instruction.
for (largeStructTy const* next_lsp = &largeStructList[1];	// Single, one time assembly instruction.
     next_lsp < &largeStructList[N];				// &largeStructList[N] is a constant, compared with a register.
     ++next_lsp)						// Single assembly instruction.
{
  largeStructTy const& ls(*lsp);		// Generates no code, internally lsp and lp are the same register.
  largeStructTy const& nextLs(*next_lsp);	// Idem, generates no code.
  // do stuff involving the reading of ls and nextLs
  // ...
}

So, that is two assembly instructions inside the loop,
an increment of register and a compare of register
with constant (address).

-- 
Carlo Wood <carlo at alinoe.com>