Why does the compiler complain when trying to construct this vector.

basically i have a code like this

Code:

---

#include <iostream>
#include <vector>
#include <iterator>
#include <algorithm>


int main()
{
        using namespace std;

        vector<int> vec(istream_iterator<int>(cin), istream_iterator<int>());
        copy(vec.begin(), vec.end(), ostream_iterator<int>(cout, "-"));
        return 0;
}

---

when I try to compile I get the errors

Quote:

---

error: request for member `begin' in `vec', which is of non-class type `std::vector<int, std::allocator<int> > ()(std::istream_iterator<int, char, std::char_traits<char>, ptrdiff_t>, std::istream_iterator<int, char, std::char_traits<char>, ptrdiff_t> (*)())' Test main.cpp line 12 1168529845046 1101

error: request for member `end' in `vec', which is of non-class type `std::vector<int, std::allocator<int> > ()(std::istream_iterator<int, char, std::char_traits<char>, ptrdiff_t>, std::istream_iterator<int, char, std::char_traits<char>, ptrdiff_t> (*)())' Test main.cpp line 12 1168529845046 1102

---

Now I usually get that error when explicitly using the () when constructing and trying to call a member for it, but this time I get it even when I propperly use a constructor with arguments.



I changed the code to this, which works

Code:

---

        vector<int> vec =
                vector<int>(istream_iterator<int>(cin), istream_iterator<int>());
        copy(vec.begin(), vec.end(), ostream_iterator<int>(cout, "-"));

---

But why?

>> vector<int> vec(istream_iterator<int>(cin), istream_iterator<int>());
This line is declaring a function named vec that returns a vector<int>. It is similar to why you cannot use empty parentheses when declaring an object (e.g. vector<int> vec();).

I don't remember where I saw the more detailed explanation, perhaps in Sutter's gotw or in the C++ FAQ Lite.

One possible solution is to wrap the arguments in an extra pair of parentheses.

Meyers's Effective STL, Item #1, "Prepare for C++'s most vexing parse."

Try this one, as laserlight suggested.

Code:

---

vector<int> vec((istream_iterator<int>(cin)), istream_iterator<int>());

---

Guru of the Week #75 is almost identical to your problem, and yes it's because it's treating vec as a function prototype.

http://www.gotw.ca/gotw/075.htm

I see, I feel kind of glad that It's not something so easily seen. Thanks for the solution.

I also noticed it works propperly if I pre-declare the istream iterators or ostream iterators before hand and pass them to the constructor.