Audison Athena wrote on 24/09/2005 19:01:05:
[...]
>
> class RandomGenObj {
[...]
> int main() {
> vector<int> v1(10, 10);
> RandomGenObj rg();
You have just declared a function named rg, that
accepts void and returns RandomGenObj by value.
C++'s ambiguity is a great thing, isn't it?
> random_shuffle(v1.begin(), v1.end(), rg);
You are passing random_shuffle the wrong type,
you are passing it a pointer to function that
returns RandomGenObj, instead of a functor (or a
function) that accepts an int and returns an int.
[...]
> Above is the test program, I compiled it under gcc version 4.0.0
> 20050519(Red Hat 4.0.0-8), and the compiler output as follow:
>
> /usr/lib/gcc/i386-redhat-linux/4.0.0/../../../../include/c
> ++/4.0.0/bits/stl_algo.h: In function ‘void
> std::random_shuffle(_RandomAccessIterator, _RandomAccessIterator,
> _RandomNumberGenerator&) [with _RandomAccessIterator =
> __gnu_cxx::__normal_iterator<int*, std::vector<int, std::allocator<int>
> > >, _RandomNumberGenerator = RandomGenObj ()()]’:
The above line tells you that the last argument to the function
is of type RandomGenObj ()(), which is a function that accepts
no arguments and returns RandomGenObj.
[...]
> ++/4.0.0/bits/stl_algo.h:1793: error: no match for ‘operator+’ in
> ‘__first + (+ __rand)()’
The above error is more hard to understand, because it does
not tell you in what way __rand's type is wrong.
[...]
> however, if I rewrite the second line in function main as follow:
> RandomGenObj rg;
> Then the compiler pass the program, everything is right.
It's because does no longer look like function declaration.
It is no longer ambiguous.
> due to my limit knowledge in C++, I can't assure if it's due to
> compiler's own problem.
> I think in syntax there's no difference between "RandomGenObj rg;" and
> "RandomGenObj rg()", since it has a default constructor.
It is ambiguous. What if you wanted to declare a function
RandomGenObj func();
and the compiler would generate an object named func instead?
Michael
