奇怪的C编译问题

typedef istream_iterator<string> isi;

// (1)
vector<string> lineas(isi(cin),isi());

// (2)
//vector<string> lineas;
//copy(isi(cin),isi(),back_inserter(lineas));

typedef vector<string>::iterator vci;
for (vci it = lineas.begin(); it != lineas.end(); ++it)
    cout << *it << endl;

但是,我在编译时遇到错误：

test.cpp: In function 'int main(int,char**)':
test.cpp:16: error: request for member 'begin' in 'lineas',which is of non-class type 'std::vector<std::basic_string<char,std::char_traits<char>,std::allocator<char> >,std::allocator<std::basic_string<char,std::allocator<char> > > >(main(int,char**)::isi,main(int,char**)::isi (*)())'
test.cpp:16: error: request for member 'end' in 'lineas',char**)::isi (*)())'

但是,如果我用(2)替换(1),它就会编译.

我正在使用g 4.4.0

怎么了？