如何使函数参数容器独立 [英] How to make function argument container independent

问题描述

我写了一个实用函数，它将获取一个元素（可以是字符串，int，double，char）的向量，并连接成一个单一的字符串并返回它。它看起来像这样：

I'm writing a utility function which will take a vector of elements (could be string, int, double, char) and concatenate into a single string and return it. It looks like this:

template<typename T>
std::string convert2Str(std::vector<T> const& vec) 
{
   std::ostringstream sStream; 
   for (size_t k=0; k<vec.size(); ++k) {
      sStream << vec[k] << " "; 
   }
   return sStream.str(); 
}

我想让这个函数更通用：

I would like to make this function more generic:

• 首先使用迭代器，而不是使用向量< T> 的索引。我试过这个
  std :: vector< T> :: const_iterator it = vec.begin（）循环之前，编译器给我一个错误：
  ：error：expected ; 之前
当我将上面的定义更改为 std :: vector< std :: string> ;: ：const_iterator it = vec.begin（）错误消失。所以，看起来我没有遵循正确的语法，请让我知道它是什么


• 第二是通过使第一个参数容器独立使函数更通用。给定任何容器（向量，列表，队列 code> deque 等）我想做同样的事情。我尝试在stackoverflow搜索这个，没有找到满意的答案。

• First use iterators instead of using indices for the vector<T>. I tried this std::vector<T>::const_iterator it = vec.begin() before the loop and the compiler gave me an error: : error: expected ; before it When I change the above defintions to std::vector<std::string>::const_iterator it = vec.begin() the error goes away. So, it looks like I'm not following correct syntax, please let me know what it is
• Second is to make the function more generic by making the first argument container independent. Given any container (vector, list, queue, deque, etc.) I want to do the same thing as above. I tried searching for this in stackoverflow and did not find satisfactory answer.

推荐答案

正如你所说，使用迭代器：

Step 1, as you said, use iterators:

template<typename T>
std::string convert2Str(std::vector<T> const& vec) 
{
   typedef std::vector<T> container;
   std::ostringstream sStream; 
   for (typename container::const_iterator it = vec.begin(); it != vec.end(); ++it) {
      sStream << *it << " "; 
   }
   return sStream.str(); 
}

步骤2，使模板参数为容器类型而不是元素类型您可以使用 value_type 获得元素类型：

Step 2, make the template argument the container type instead of the element type (you can get the element type back with value_type:

template<typename container>
std::string convert2Str(container const& vec)
{
   typedef container::value_type T; // if needed
   std::ostringstream sStream; 
   for (typename container::const_iterator it = vec.begin(); it != vec.end(); ++it) {
      sStream << *it << " "; 
   }
   return sStream.str(); 
}

++ 0x，这变得更简单（并且不需要 typename ）：

In C++0x, this gets even simpler (and typename is not needed):

template<typename container>
std::string convert2Str(container const& vec)
{
   using std::begin;
   using std::end;
   std::ostringstream sStream;
   for (auto it = begin(vec); it != end(vec); ++it) {
      typedef decltype(*it) T; // if needed
      sStream << *it << " "; 
   }
   return sStream.str(); 
}

除了其他优点， std :: begin 和 std :: end 用于原始数组。

Among other advantages, std::begin and std::end work for raw arrays.

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