c++ - std::time_get - 来自 std::cin 的输入正常；来自 std::istringstream 的输入给出错误

Question

我已使用 std::time_get::get_date() 方法从以下来源读取日期:

1. std::cin

2. std::istringstream 基于 string s，其值已从 std::getline(std::cin, s) 获得.

来自 std::cin 的输入工作正常；日期被正确读取并打印得很好。

然而，来自 std::istringstream 的输入给出错误；日期读取不正确。

以下是 std::istringstream 来源的代码:

http://coliru.stacked-crooked.com/a/31704818a11d5629

vector<string> locales {"C"};

/// Get I/P from a string.
void IPFromStr()
{
    cout << "\nI/P from a string ... " << endl;

    /// For each locale name
    for (const auto& locs : locales)
    {
        cout << "locale name: " << locs << endl;

        try
        {
            /// Create the locale.
            locale loc {locs};

            /// Read date/time parts from a string.
            ReadDtPartFromStr(loc);
        }
        catch (const exception& e)
        {
            cerr << " Exception: " << e.what()
                 << endl << endl;
        }
    }
}

/// Read date/time parts from a string.
void ReadDtPartFromStr(locale& loc)
{
    /// Get the time_get<> facet.
    const time_get<char>& tg =
              use_facet<time_get<char>> (loc);

    /// I/P string variable for the read date part.
    string dtpart {};

    /// output arguments for the time_get<> facet
    struct tm d {};                             /// time
    ios_base::iostate err = ios_base::goodbit;  /// good

    getline(cin, dtpart);

    cout << " dtpart: " << dtpart << endl;

    /// Get an istringstream for the read date part
    istringstream isdtpart {dtpart};

    isdtpart.imbue(loc);

    istreambuf_iterator<char> frm(isdtpart), end;

    /// Read the date part.
    tg.get_date(frm, end,
                isdtpart,
                err,
                &d);

    /// Print the date read.            
    Print(err, d);
}

Print() 函数是:

/// Print the date read.
void Print(ios_base::iostate& err, tm& d)
{
    if (err)
       cout << " error while reading input" << endl;
    else
       cout << " yyyy/mm/dd hh:mm:ss  : " 
            << d.tm_year + 1900 << '/'
            << d.tm_mon + 1     << '/'
            << d.tm_mday        << ' '
            << d.tm_hour        << ':'
            << d.tm_min         << ':'
            << d.tm_sec
            << endl;
}

给定以下 std::cin 输入:

01/26/2018

我得到以下输出:

I/P from a string ... 

locale name: C
 dtpart: 01/26/2018
 error while reading input

相同的输入适用于直接从 std::cin 读取的类似函数。

为什么我从std::istringstream读取时会出现这个错误？

Answer 1

您认为 eof 意味着发生了错误。

替换这个:

if (err)

与

if (err & (ios::failbit | ios::badbit))