How to load stream cin into vector

Question

I want to load a vector with integers from cin. The following code works:

std::istream_iterator< int > iterBegin( std::cin ), iterEnd;
vector< int > v( iterBegin, iterEnd );

However, when I try to write it more succinctly, it fails:

vector< int > v(std::istream_iterator< int >(std::cin), 
                std::istream_iterator< int >() );

Any ideas?

Answer 1

As IgorTandetnik pointed out, you ran into C++'s Most vexing parse. The solution (if your compiler understands C++11) is to use uniform initialization syntax.

clang has a suggestion that will work even in C++98:

cin-vec.cc:7:21: warning: parentheses were disambiguated as a function declaration [-Wvexing-parse]
std::vector< int > v(std::istream_iterator< int >(std::cin),
                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cin-vec.cc:7:22: note: add a pair of parentheses to declare a variable
std::vector< int > v(std::istream_iterator< int >(std::cin),
                     ^
                     (                                     )
cin-vec.cc:12:19: error: member reference base type 'std::vector<int> (std::istream_iterator<int>, std::istream_iterator<int> (*)())' is not a structure or union
    std::cout << v.size();
                 ~^~~~~

ie change your code to:

std::vector< int > v((std::istream_iterator< int >(std::cin)),
                std::istream_iterator< int >() );