std::stringstream 作为函数的参数 [英] std::stringstream as parameter to a function

问题描述

我有一个 std::vectortemp_results 并且我希望使用 std::for_each 来遍历这个向量并连接一个字符串，所以我炮制了以下结构:

I have a std::vector<std::string> temp_results and I wish to use std::for_each to go through this vector and concatenate a string, so I concocted the following construction:

std::stringstream ss;
std::string res = std::for_each(temp_results.begin(), temp_results.end(), boost::bind(addup, _1, ss));

std::string addup(std::string str, std::stringstream ss)
{
    ss << str;
    ss << ";";

    return ss.str;
}

我收到以下错误，这超出了我的理解:

I get the following error, which is beyond my understanding:

error C2475: 'std::basic_stringstream<_Elem,_Traits,_Alloc>::str' : forming a pointer-to-member requires explicit use of the address-of operator ('&') and a qualified name
        with
        [
            _Elem=char,
            _Traits=std::char_traits<char>,
            _Alloc=std::allocator<char>
        ]

谁能解释一下哪里出了问题?

Could someone please explain what is wrong?

推荐答案

如果，通过编写 return ss.str; 你打算从 str 调用成员函数 strcode>std::stringstream，那么你缺少一对括号:

If, by writing return ss.str; you intend to call the str member function from std::stringstream, then you are missing a pair of parenthesis :

return ss.str();

此外，您的代码可能不会按照您的预期运行.如果您希望每次调用 addup 都在同一个 std::stringstream 实例上工作，则必须通过引用来获取它:修改 addup签名并在 boost::bind 中的 ss 参数周围添加一个 boost::ref().

Also, your code probably won't do what you expect. If you want every call to addup to work on the same std::stringstream instance, you have to take it by reference : modify the addup signature and add a boost::ref() around the ss parameter in the boost::bind.

这是一个工作版本，我认为它可以满足您的期望:

Here is a working version which I presume does what you expect :

void addup(std::string str, std::stringstream &ss)
{
    ss << str;
    ss << ";";
}

int main() 
{
    std::vector<std::string> temp_results;
    /* ... */

    std::stringstream ss;
    std::for_each(temp_results.begin(), temp_results.end(), boost::bind(addup, _1, boost::ref(ss)));
    std::cout << ss.str() << std::endl;
}

使用 boost::lambda 的替代方法:

std::for_each(temp_results.begin(), temp_results.end(), ss << boost::lambda::_1 << ';');

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