c++ - boost::date_time::days_until_weekday 的编译错误

Question

我目前正在研究 boost::date_time。这样做时，我遇到了 days_until_weekday ( documentation link ) 函数，它对我来说非常有用。不幸的是，我从以下代码片段中得到编译时错误

date f(date d){
    return next_weekday(d,  boost::date_time::weekdays::Friday);
}

读书

> In file included from
> /usr/include/boost/date_time/gregorian/gregorian_types.hpp:25:0,
>                  from /usr/include/boost/date_time/posix_time/posix_time_config.hpp:18,
>                  from /usr/include/boost/date_time/posix_time/posix_time_system.hpp:13,
>                  from /usr/include/boost/date_time/posix_time/ptime.hpp:12,
>                  from /usr/include/boost/date_time/posix_time/posix_time.hpp:15,
>                  from prog.cpp:3: /usr/include/boost/date_time/date_generators.hpp: In instantiation of
> 'typename date_type::duration_type
> boost::date_time::days_until_weekday(const date_type&, const
> weekday_type&) [with date_type = boost::gregorian::date; weekday_type
> = boost::date_time::weekdays; typename date_type::duration_type = boost::gregorian::date_duration]':
> /usr/include/boost/date_time/date_generators.hpp:488:34:   required
> from 'date_type boost::date_time::next_weekday(const date_type&, const
> weekday_type&) [with date_type = boost::gregorian::date; weekday_type
> = boost::date_time::weekdays]' prog.cpp:11:67:   required from here /usr/include/boost/date_time/date_generators.hpp:452:37: error:
> request for member 'as_number' in 'wd', which is of non-class type
> 'const boost::date_time::weekdays'
>      duration_type dd(wd.as_number() - d.day_of_week().as_number());

去here粘贴我的代码。

由于导致错误的代码段太短，我真的没有办法解决这个问题。

顺便说一下，我正在使用 clang 3.7.0 的 boost 1.60.0。

Answer 1

您需要将 date_time 枚举转换为与传递给函数的 weekday_type 所期望的接口(interface)相匹配的对象。使用 greg_weekday 函数为您执行此操作，例如:

    return next_weekday(d, boost::gregorian::greg_weekday(boost::date_time::Friday));

在 VS2015 和 boost 1.53 下为我编译。

此函数的文档链接: greg_weekday