c++：打印 STL 列表

Question

我正在浏览 STL 列表，并尝试将列表实现为类型类而不是 int 或任何其他数据类型。下面是我尝试编译的代码

#include <iostream>
#include <list>

using namespace std;

class AAA {
public:
    int x;
    float y;
    AAA();
};

AAA::AAA() {
    x = 0;
    y = 0;
}

int main() {
    list<AAA> L;
    list<AAA>::iterator it;
    AAA obj;

    obj.x=2;
    obj.y=3.4;
    L.push_back(obj);

    for (it = L.begin(); it != L.end(); ++it) {
        cout << ' ' << *it;
    }
    cout << endl;
}

但它在该行中给出错误：

cout<<' '<<*it;

错误是

In function 'int main()':
34:13: error: cannot bind 'std::basic_ostream<char>' lvalue to    'std::basic_ostream<char>&&'
In file included from /usr/include/c++/4.9/iostream:39:0,
             from 1:
/usr/include/c++/4.9/ostream:602:5: note: 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 = AAA]'
 operator<<(basic_ostream<_CharT, _Traits>&& __os, const _Tp& __x)
 ^

实际上我想使用上面的代码打印列表的内容。有人可以帮我解决这个问题吗？？

Answer 1

您尝试将AAA 类型的对象输出到std::ostream。为此，您需要为operator<< 编写重载。像这样的：

std::ostream& operator<< (std::ostream& stream, const AAA& lhs)
{
    stream << lhs.x << ',' << lhs.y;
    return stream;
}