我可以使用stream运算符绑定吗？ [英] Can I use stream operator with bind?

问题描述

我仍然在学习c ++ 11的功能，如何正确使用绑定。这是一个实验：

I am still learning c++11 features around how to use bind properly. Here is an experiment:

using namespace std::placeholders;
using namespace std;

struct MyType {};

ostream& operator<<(ostream &os, const MyType &n)
{
    os << n;
    return os;
}

int main()
{
    std::vector<MyType> vec;

    std::for_each(vec.begin(), vec.end(), std::bind(operator<<, std::ref(std::cout), _1));

    return 0;
}

我得到clang编译错误：

I get clang compile error:

error: no matching function for call to 'bind'
    std::for_each(vec.begin(), vec.end(), std::bind(operator<<, std::ref(std::cout), _1));

我想bind不能区分函数运算符<<

I guess bind cannot distinguish the function operator<< defined in my file from those pre-defined.

但我不知道它是否可以做，只是我做错了吗？

But I wonder if it actually can be done and just I did it wrong?

感谢ISARANDI，prefixing ::修复了问题。但是如何在同一个命名空间我有重载的函数：

Thanks ISARANDI, prefixing :: fixed the problem. But how about at the same namespace I have overloaded functions:

using namespace std::placeholders;
using namespace std;

struct MyType {};
struct MyType2 {};

ostream& operator<<(ostream &os, const MyType &n)
{
    os << n;
    return os;
}

ostream& operator<<(ostream &os, const MyType2 &n)
{
    os << n;
    return os;
}

int main()
{
    std::vector<MyType> vec;

    std::for_each(vec.begin(), vec.end(), std::bind(::operator<<, std::ref(std::cout), _1));

    return 0;
}

在这种情况下，即使使用全局命名空间，我仍然会遇到编译错误。 。

In this case, I still get that compile error even with the global namespace.. Is there a solution here?

好的，想出来，我需要把它：

OK, figured out, I need to cast it:

std::for_each(vec.begin(), vec.end(), std::bind((ostream&(ostream&, const MyType&))::operator<<, std::ref(std::cout), _1));

推荐答案

因为 using namespace std ; 运算符<< 有多个重载。
要显式选择您的版本，请写

Because of using namespace std; operator<< has multiple overloads. In order to explicitly select your version, write

std::for_each(vec.begin(), vec.end(), std::bind(::operator<<, std::ref(std::cout), _1));

前缀 :: 全局命名空间。

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