C ++ /升压：编写一个更强大的sscanf更换 [英] C++/Boost: Writing a more powerful sscanf replacement

问题描述

我想C ++编写一个函数来替换C的sscanf的是分配火柴迭代器。

I want to write a function in C++ to replace C's sscanf that assigns the matches to iterator.

基本上，我想是这样的：

Basically, I want something like:

string s = "0.5 6 hello";
std::vector<boost::any> any_vector;
sscanv(s, "%f %i %s", any_vector);
cout << "float: " << any_cast<float>(any_vector[0]);
cout << "integer: " << any_cast<integer(any_vector[1]);
cout << "string: " << any_cast<string>(any_vector[2]);

的具体细节可能会有所不同，但你的想法。实施任何想法？

The exact details may vary, but you get the idea. Any ideas for implementation?

选项到目前为止随着问题至今：

Options so far along with problems so far:

• 的std :: istringstream ：有没有操纵匹配的恒定前pressions


• Boost.Regex ​​：不知道这是否会工作，似乎对这个复杂得多必要


• Boost.Spirit ：不认为这会为动态生成的格式字符串工作，它也似乎更复杂然后必要


• 的sscanf ：这是可行的，而且是不规范等，并使用以来在编译时确定的参数个数这将需要大量的开销

• std::istringstream: there's no manipulator for matching constant expressions
• Boost.Regex: not sure if this will work and it seems much more complicated than necessary for this
• Boost.Spirit: don't think this will work for dynamically generated format strings and it also seems more complicated then necessary
• sscanf: it would work, but is non-standard, etc, and using it would require a lot of overhead since the number of arguments is determined at compile time

推荐答案

有什么看法？

void sscanf(std::string str,
            const std::string& format,
            std::vector<boost::any>& result)
{
  std::string::const_iterator i = format.begin();
  while (i != format.end())
  {
    if (*i == '%')
    {
      ++i; // now *i is the conversion specifier
      char specifier = *i;

      ++i; // now *i is the next seperator
      std::string extract = str.substr(0, str.find(*i));

      switch (specifier) 
      {
        // matching an integer
        case 'i':
          result.push_back(boost::lexical_cast<int>(extract));
          break;
        // matching a floating point number
        case 'a': case 'e': case 'f': case 'g':
          result.push_back(boost::lexical_cast<float>(extract));
          break;
        // matching a single character
        case 'c':
          result.push_back(boost::lexical_cast<char>(extract));
          break;
        // matching a string
        case 's':
          result.push_back(extract);
          break;
        // Invalid conversion specifier, throwing an exception
        default:
          throw std::runtime_error("invalid conversion specifier");
          break;
      }
    }
    else
    {
      // if it's not a %, eat!
      str.erase(0, str.find(*i)+1);
      ++i;
    }
  }
}

有些转化符缺少 - 但主要是它的工作原理。

Some conversions specifiers are missing – but principally it works.

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