Re: C++ Primer ex 9.14
James Kanze wrote:
it only happens to those with none parameter like the latter
one you wrote.
std::istream_iterator< std::string >()
would be a declaration---in the context of a function parameter,
declaration of what?
a function or a pointer to function?
I think this needs more discussion:
see:
template <class F = void()>
struct Func;
template <class RET, class ARG>
struct Func <RET(ARG)>
{
};
Func<int(int)> int_int_f;
here "int(int)" is a type I think, not a variable.
If you say "it differs if context differs", would you tell me more?
it's the equivalent of:
std::istream_iterator< std::string >(*ptrToFnc)()
actually, they are not equivent
int (f)(int); : f is typeof function
int (*pf) (int); : pf is typeof pointer to function.
And while I think you're right for
std::istream_iterator< std::string >( std::cin ),
something like:
std::istream_iterator< std::string >( someFile ),
is definitely a declaration.
Technically, too, it should be sufficient to disambiguate any
one of the parameters; adding the parentheses to just one of the
parameters should suffice. But I've had problems with this in
the past, and have gotten into the habit of adding them more or
less systematically, whenever there might be an ambiguity.
yeh, it depends on the compiler, I think, though I don't use many compilers.
maybe adding "()" around the variable is still not the ultimate
solution, it *may* (I don't have any test case) still fail to compile on
some compilers.
the most portable way, but not so elegant would be
std::istream_iterator< std::string > end;
vector<...> vec(
...
end
);
(This is really something that needs fixing, although I don't
have a good solution. Imagine the poor beginner, who originally
writes the code without the extra parentheses, using std::cin,
and it works fine. He then replaces std::cin with a file, and
suddenly gets compiler errors when he tries to use vec, further
down in his code.)
:-), considerate
--
Thanks
Barry