重构“哑”函数转换为通用的STL风格与迭代器到容器 [英] Refactoring a "dumb" function into generic STL-style with iterators to containers

问题描述

我已经设法围绕一些C ++的功能性能力（for_each，映射函数，使用迭代器...），但是模板和函数参数列表的构造，用于接收通用容器和迭代器仍然逃避了我。我有一个实际的例子，我希望有人可以为我说明：

I've managed to wrap my head around some of C++'s functional capacities (for_each, mapping functions, using iterators...) but the construction of the templates and function argument lists for taking in generic containers and iterators still eludes me. I have a practical example I'm hoping someone can illustrate for me:

采取以下函数处理一个传入的std :: vector，并建立一个运行的许多数据 - 进程的点/迭代：

Take the following function that processes an incoming std::vector and builds a running total of many data-points/iterations of a process:

/* the for-loop method - not very savvy */
void UpdateRunningTotal (int_vec& total, int_vec& data_point) {
  for (int i = 0; i < V_SIZE; i++) {
    total[i] += data_point[i];
  }
}

typedef int_vec std::vector<int>;
int_vec running_total (V_SIZE, 0);  // create a container to hold all the "data points" over many iterations
/* further initialization, and some elaborate loop to create data points */

UpdateRunningTotal (running_total, iteration_data);
/* further processing */

上面的工作，一个函数，它接受迭代器并执行这个求和。更好的是，具有推导类型的通用参数列表，而不是指定容器类型，即：

The above works, but I'd much rather have a function that takes iterators and performs this summation. Even better, have a generic parameter list with the type deduced instead of specifying the container type, i.e.:

UpdateRunningTotal (iteration_data.begin(), iteration_data.end(), running_total.begin());

我真的在这一点上迷失了，需要一些指导才能找到如何定义模板参数列表使函数通用。模板和函数定义会是什么样子？我已经熟悉如何使用STL功能执行这个特定的任务 - 我正在寻找通用函数/模板定义的插图。

I'm really lost at this point and need a little guidance to find how to define the template and argument lists to make the function generic. What would the template and function definition look like? I'm already familiar with a way to perform this specific task using STL functionality - I'm looking for illustration of the generic function/template definition.

推荐答案

您可以使用 std :: transform 和 std :: plus ：

You could use std::transform and std::plus:

std::transform(iteration_data.begin(), iteration_data.end(),
                running_total.begin(), iteration_data.begin(), std::plus<int>());

在您的函数中，它将是：

And in your function, that would be:

template <typename Iter1, typename Iter2>
void UpdateRunningTotal(Iter1 pBegin, Iter1 pEnd, Iter2 pBegin2)
{
    typedef typename std::iterator_traits<Iter1>::value_type value_type;

    std::transform(pBegin, pEnd, pBegin2, pBegin, std::plus<value_type>());
}

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