将单个字符转换为std::string prepends\x01

我试图从一个无序的映射中接收值 std::string 作为键,其中一些字符串只包含一个字符。我所有的输入都来自 std::stringstream 从中获取每个值并将其转换为char,然后使用
std::string result {1, character}; documentation 和 this answer .

为什么会发生这种情况,我该如何解决?

#include <iostream>
#include <sstream>
#include <unordered_map>

int main()
{
    const std::unordered_map<std::string, int> map = { {"H", 1}, {"BX", 2} };

    std::stringstream temp {"Hello world!"};
    char character = static_cast<char>(temp.get());  // character is 'H'
    std::string result {1, character};               // string contains "\x01H"

    std::cout << result << " has length " << result.size() << std::endl; // H has length 2
    std::cout << map.at(result) << std::endl;        // unordered_map::at: key not found
}