boost::posix_time::time_方面和boost::posix_time::time_input_方面之间的“%f”行为不一致

我正在试着转换一个 boost::posix_time::ptime 转换为特定的字符串格式(扩展ISO),然后返回到 boost::posix_time::ptime .

令人惊讶的是,它看起来像 boost::posix_time::time_facet %f 000000 到 999999 (不带小数点分隔符)。要不是 boost::posix_time::time_input_facet ,意思是 .000000 .999999 (带小数点分隔符)。

#include <boost/date_time/posix_time/posix_time.hpp>
#include <iostream>

int main( int argc, char** argv )
{
    auto now = boost::posix_time::second_clock::local_time();

    std::stringstream outStr;
    {
        boost::posix_time::time_facet* facet = new boost::posix_time::time_facet();
        facet->format("%Y-%m-%dT%H:%M:%S.%f");
        outStr.imbue(std::locale(std::locale::classic(), facet));
        outStr << now;
    }
    std::cout << outStr.str() << std::endl;

    {
        static const std::string format = "%Y-%m-%dT%H:%M:%S.%f";
        const std::locale loc = std::locale(std::locale::classic(), new boost::posix_time::time_input_facet(format));
        std::istringstream is(outStr.str());
        is.imbue(loc);
        boost::posix_time::ptime converted;
        is >> converted;
        std::cout << converted << std::endl;
    }

    {
        static const std::string format = "%Y-%m-%dT%H:%M:%S%f";
        const std::locale loc = std::locale(std::locale::classic(), new boost::posix_time::time_input_facet(format));
        std::istringstream is(outStr.str());
        is.imbue(loc);
        boost::posix_time::ptime converted;
        is >> converted;
        std::cout << converted << std::endl;
    }

    return 0;
}

This outputs

2019-04-30T12:23:29.000000
not-a-date-time
2019-Apr-30 12:23:29

2019-04-30T12:23:29.000000
2019-Apr-30 12:23:29
not-a-date-time

我用的是boost 1.68。

我是做错了什么,还是这是一个错误 或 boost::posix_time::input_time_facet ?

注意:'%F'没有此问题。