range -v3组合在使用ranges::views:: counts(1)时产生错误

Question

我正在使用范围库(eric niebler范围)，我试图写一个范围组合，但我使用的范围::视图::计数(1)选项不起作用。

我试图从右边忽略，到目标时间减去1个进一步的时间段(5分钟)。然后，提取下一个1x值。

这是一个可视化的例子(与下面的代码无关)，我试图实现的。

time
1:00 1:01 1:02 1:03 1:04 1:05 1:06 1:07 1:08 1:09 1:10 1:11 1:12 1:13 1:14 1:15 1:16
          ^start_reading
^target_time
^target_time minus 1x5mins periods, 
start extraction here 
^extract the value associated with this time

到目前为止，我开发的代码如下:

#include <fmt/format.h>
#include <range/v3/all.hpp>
#include <chrono>
#include <vector>
#include <iostream>
struct th {
std::chrono::system_clock::time_point timestamp;
double h;
};
constexpr auto period_start(const std::chrono::system_clock::time_point timestamp,
const std::chrono::minutes timeframe)
-> std::chrono::system_clock::time_point
{
using namespace std::chrono;
const auto time = hh_mm_ss{floor<minutes>(timestamp - floor<days>(timestamp))};
return timestamp - (time.minutes() % timeframe);
}
auto main() -> int
{
using namespace std::chrono_literals;
namespace views = ranges::views;
const auto timeframe = 5min;
{ 
const auto tp = std::chrono::system_clock::from_time_t(0); // just used for populating the example vector
const auto timestamped_h = std::vector<th>{
{tp + 0min , 1.0}, {tp + 1min , 1.1}, {tp + 3min , 1.2}, {tp + 4min , 1.2},
{tp + 5min , 0.8}, {tp + 6min , 0.9}, {tp + 7min , 1.0},
{tp + 10min, 1.1}, {tp + 11min, 1.3}, {tp + 12min, 1.2}, {tp + 13min, 1.1}, {tp + 14min, 0.9},
{tp + 15min, 0.8}, {tp + 16min, 1.4}, {tp + 17min, 1.3}, {tp + 18min, 1.6}, {tp + 19min, 1.5}
};
const auto target_tp = tp + 17min;
const auto remove_candle = [target_tp,timeframe](const auto& lhs) { 
return lhs.timestamp >= period_start(target_tp - 1* timeframe,timeframe); 
};
auto pivots = timestamped_h 
| views::reverse
| views::remove_if(remove_candle)
//| views::filter(remove_candle)
| ranges::views::counted(1);
for(auto p : pivots)
std::cout << p.h << std::endl;
}
}

但是ranges::views:: counts(1)选项会产生以下错误:error: no match for call to '(const ranges::views::counted_fn) (int)'

此处提供步道区域

请问我做错了什么?

Answer 1

我需要的是::count，是::take。最终结果:

auto pivots = timestamped_h 
| views::reverse
| views::remove_if(remove_candle)
| ranges::views::take(1);