c++ - 将 std::string 转换为任何数字类型或 std::string 的成员函数模板

Question

请考虑成员函数模板。我的问题嵌入在评论表单中。

template<typename T>
GetValueResult GetValue(
                          const std::string &key,
                          T &val,
                          std::ios_base &(*manipulator)(std::ios_base &) = std::dec
                       )
{
   // This member function template is intended to work for all built-in
   // numeric types and std::string. However, when T = std::string, I get only
   // the first word of the map element's value. How can I fix this?

   // m_configMap is map<string, string>
   ConfigMapIter iter = m_configMap.find(key);

   if (iter == m_configMap.end())
      return CONFIG_MAP_KEY_NOT_FOUND;

   std::stringstream ss;
   ss << iter->second;

   // Convert std::string to type T. T could be std::string.
   // No real converting is going on this case, but as stated above
   // I get only the first word. How can I fix this?
   if (ss >> manipulator >> val)
      return CONFIG_MAP_SUCCESS;
   else
      return CONFIG_MAP_VALUE_INVALID;
}

Answer 1

流上的<<and>>运算符旨在处理由空格分隔的标记。所以如果一个字符串看起来像 "1 2" 那么你stringstream只会读入1第一个<<。

如果您想要多个值，我建议您在流上使用循环。这样的事情可能会...

//stringstream has a const string& constructor
std::stringstream ss(iter->second); 

while (ss >> manipulator >> value) { /* do checks here /* }

有了这个，我建议你看看 Boost，特别是lexical_cast，它可能会做你想要的开箱即用。