boost :: lexical_cast无法识别重载的istream运算符 [英] boost::lexical_cast not recognizing overloaded istream operator

问题描述

我有以下代码:

#include <iostream>
#include <boost\lexical_cast.hpp>

struct vec2_t
{
    float x;
    float y;
};

std::istream& operator>>(std::istream& istream, vec2_t& v)
{
    istream >> v.x >> v.y;

    return istream;
}

int main()
{
    auto v = boost::lexical_cast<vec2_t>("1231.2 152.9");

    std::cout << v.x << " " << v.y;

    return 0;
}

我从Boost收到以下编译错误:

I am receiving the following compile error from Boost:

错误1错误C2338:目标类型都不是std :: istream able nor std::wistream able

这似乎很简单，在过去的一个小时里，我一直把头撞在桌子上.任何帮助将不胜感激！

This seems straightforward enough, and I have been hitting my head against the desk for the last hour. Any help would be appreciated!

编辑:我正在使用Visual Studio 2013.

I am using Visual Studio 2013.

推荐答案

正在进行两阶段查找.

您需要使用ADL启用过载，因此lexical_cast将在第二阶段找到它.

You need to enable the overload using ADL, so lexical_cast will find it in the second phase.

因此，您应该将重载移至名称空间mandala

So, you should move the overload into namespace mandala

这是一个完全固定的示例(您还应该使用std::skipws):

Here's a completely fixed example (you should also use std::skipws):

在Coliru上直播

#include <iostream>
#include <boost/lexical_cast.hpp>

namespace mandala
{
    struct vec2_t {
        float x,y;
    };    
}

namespace mandala
{
    std::istream& operator>>(std::istream& istream, vec2_t& v) {
        return istream >> std::skipws >> v.x >> v.y;
    }
}

int main()
{
    auto v = boost::lexical_cast<mandala::vec2_t>("123.1 15.2");
    std::cout << "Parsed: " << v.x << ", " << v.y << "\n";
}

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