c++ - 当我尝试使用 sstream 和 facet 将 Boost Time_duration 转换为字符串时，我没有得到所需的格式

Question

我正在尝试将 boost::posix_time::time_duration 对象转换为 "%H%M"形式的 string。问题是对话是不工作就好像它不存在一样。

• 我用来将 Duration 转换为字符串的函数是 convert_duration_to_string

我也尝试过这种方式，如下面的函数所示。它可以解决问题。但它太丑了。假设将来我们必须更改日期格式。在这种情况下，我们也必须更改函数内的代码。

std::string convert_duration_to_string(Duration duration) {
  std::ostringstream os;
  os << std::setfill('0') << std::setw(2) << duration.hours()
     << std::setfill('0') << std::setw(2) << duration.minutes();
  return os.str();
}

---

#include <boost/date_time/local_time/local_time.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>
#include "boost/date_time/gregorian/gregorian.hpp"

#include <iostream>
#include <sstream>

typedef boost::posix_time::time_duration Duration;

boost::posix_time::ptime parse_time_object(const std::string &time,
                                           const std::string &format) {
  std::stringstream ss;
  ss << time.c_str();
  ss.imbue(std::locale(
      std::locale::classic(),
      new boost::local_time::local_time_input_facet(format.c_str())));
  boost::posix_time::ptime time_object;
  ss >> time_object;

  return time_object;
}


std::string convert_duration_to_string(Duration           duration,
                                       const std::string &format) {
  std::ostringstream os;
  os.imbue(std::locale(std::locale::classic(),
                       new boost::posix_time::time_facet(format.c_str())));
  os << duration;
  return os.str();
}


int main (){
    Duration duration = parse_time_object("0740", "%H%M").time_of_day();
    //[...] PLENTY OF THINGS CAN HAPPEN IN HERE THE DATE CAN GO through A 
    // WHOLE PIPELINE AND COME BACK
    std::cout << convert_duration_to_string(duration,"%H%M") << std::endl; //Should Pring 0740. instead it is printing 07:40:00
    return 0;
}

Answer 1

您正在输出持续时间，因此您需要更改持续时间格式。仅使用默认持续时间格式创建时间面是不够的。 IOW 像这样修改你的代码......:

std::string convert_duration_to_string(Duration           duration,
                                       const std::string &format) {
    std::ostringstream os;
    auto f = new boost::posix_time::time_facet(format.c_str());
    f->time_duration_format(format.c_str());
    os.imbue(std::locale(std::locale::classic(), f));
    os << duration;
    return os.str();
}

...似乎work .