<分区>
我想弄明白为什么下面的代码不能编译
#include <vector>
#include <ostream>
#include <iterator>
#include <iostream>
template <class ostream>
ostream& operator<<(ostream& o, const std::vector<double>& data)
{
std::copy(data.begin(), data.end(), std::ostream_iterator<double>(o, " "));
return o;
}
template<class ostream>
ostream& operator<<(ostream& o, const std::vector<std::vector<double>>& data)
{
std::copy(data.begin(), data.end(), std::ostream_iterator<std::vector<double>>(o, "\n"));
return o;
}
int main(int argc, char **argv)
{
std::vector<std::vector<double>> vecvec = {{1,2,3},
{4,5,6}};
std::cout << vecvec << std::endl;
}
我认为既然我已经定义了一个 operator<<对于 vector<double>我应该可以利用 ostream_iterator
相反，我得到了一个编译错误，如果我将代码更改为以下内容，那么一切都可以正常编译。
#include <vector>
#include <ostream>
#include <iterator>
#include <iostream>
template <class ostream>
ostream& operator<<(ostream& o, const std::vector<double>& data)
{
std::copy(data.begin(), data.end(), std::ostream_iterator<double>(o, " "));
return o;
}
template<class ostream>
ostream& operator<<(ostream& o, const std::vector<std::vector<double>>& data)
{
/** changed to manually looping **/
for (const auto& line : data)
{
o << line << "\n";
}
return o;
}
int main(int argc, char **argv)
{
std::vector<std::vector<double>> vecvec = {{1,2,3},
{4,5,6}};
std::cout << vecvec << std::endl;
}
我做错了什么？
最重要的是...谁能向我解释为什么 ostream_iterator这里编译失败？
我可以找到解决方法并解决我的问题，但似乎我还没有完全理解 ostream_iterator 是如何产生的作品
这是编译器(gcc 4.8.5)的输出
In file included from /opt/compiler-explorer/gcc-4.8.5/include/c++/4.8.5/iterator:66:0,from <source>:3:
/opt/compiler-explorer/gcc-4.8.5/include/c++/4.8.5/bits/stream_iterator.h: In instantiation of 'std::ostream_iterator<_Tp, _CharT, _Traits>& std::ostream_iterator<_Tp, _CharT, _Traits>::operator=(const _Tp&) [with _Tp = std::vector<double>; _CharT = char; _Traits = std::char_traits<char>]':
/opt/compiler-explorer/gcc-4.8.5/include/c++/4.8.5/bits/stl_algobase.h:335:18: required from 'static _OI std::__copy_move<false, false, std::random_access_iterator_tag>::__copy_m(_II, _II, _OI) [with _II = std::vector<double>*; _OI = std::ostream_iterator<std::vector<double> >]'
/opt/compiler-explorer/gcc-4.8.5/include/c++/4.8.5/bits/stl_algobase.h:390:70: required from '_OI std::__copy_move_a(_II, _II, _OI) [with bool _IsMove = false; _II = std::vector<double>*; _OI = std::ostream_iterator<std::vector<double> >]'
/opt/compiler-explorer/gcc-4.8.5/include/c++/4.8.5/bits/stl_algobase.h:428:38: required from '_OI std::__copy_move_a2(_II, _II, _OI) [with bool _IsMove = false; _II = __gnu_cxx::__normal_iterator<std::vector<double>*, std::vector<std::vector<double> > >; _OI = std::ostream_iterator<std::vector<double> >]'
/opt/compiler-explorer/gcc-4.8.5/include/c++/4.8.5/bits/stl_algobase.h:460:17: required from '_OI std::copy(_II, _II, _OI) [with _II = __gnu_cxx::__normal_iterator<std::vector<double>*, std::vector<std::vector<double> > >; _OI = std::ostream_iterator<std::vector<double> >]'
<source>:17:96: required from 'ostream& operator<<(ostream&, std::vector<std::vector<double> >&) [with ostream = std::basic_ostream<char>]'
<source>:26:18: required from here
/opt/compiler-explorer/gcc-4.8.5/include/c++/4.8.5/bits/stream_iterator.h:198:13: error: cannot bind 'std::ostream_iterator<std::vector<double> >::ostream_type {aka std::basic_ostream<char>}' lvalue to 'std::basic_ostream<char>&&'
*_M_stream << __value;
^
In file included from <source>:2:0:
/opt/compiler-explorer/gcc-4.8.5/include/c++/4.8.5/ostream:602:5: error: initializing argument 1 of 'std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&&, const _Tp&) [with _CharT = char; _Traits = std::char_traits<char>; _Tp = std::vector<double>]'
operator<<(basic_ostream<_CharT, _Traits>&& __os, const _Tp& __x)
^
Compiler returned: 1