Visual 2015上的std :: get_time不会在不正确的日期失败 [英] std::get_time on Visual 2015 does not fail on incorrect date

问题描述

我正在Windows上使用Visual Studio 2015执行以下代码。基本上，我使用 std :: get_time 来解析日期，但是当日期无效时，例如，如果一天大于31，似乎并没有在流中设置失败位。

I'm executing the following code on Windows with Visual Studio 2015. Basically I use std::get_time to parse a date, but when the date is invalid, for example, a day greater than 31, it does not seem to set the fail bit on the stream.

我已经在带有g ++ 5.4.0的Ubuntu上进行了尝试，它设置了失败位并显示解析失败！。这是Windows上的错误，还是我做错了事。

I have tried this on Ubuntu with g++ 5.4.0 and it sets the fail bit and prints "Parsing failed!". Is this a bug on Windows or am I doing something wrong.

预先感谢！

std::string date = "2019-2-37 23:00:00"; // day (37) is wrong. 
std::string format = "%Y-%m-%d %H:%M:%S";
std::tm tm_object{};
std::istringstream input(date);        
input.imbue(std::locale(std::setlocale(LC_ALL, nullptr)));
input >> std::get_time(&tm_object, format.c_str());
if (input.fail()) 
{
    std::cout << "Parsing failed!";
}
else
{
    std::cout << "Parsing ok!\n";
    std::cout << "Day is : " << tm_object.tm_mday;
}

推荐答案

您可以使用 Howard Hinnant在Windows上免费的，开放源代码的仅标头日期时间库，可为您提供所需的行为。语法略有不同，并且易于使用，并且与< chrono> 兼容。与C ++标准的时间解析部分相比，它的文档和说明也更好。

You can use Howard Hinnant's free, open-source header-only datetime library on Windows to give you the desired behavior. The syntax is only slightly different, and it is much easier to use, and compatible with <chrono>. It is also better documented and specified than the time-parsing parts of the C++ standard.

#include "date.h"
#include <iostream>
#include <sstream>
#include <string>

int
main()
{
    std::string date = "2019-2-37 23:00:00"; // day (37) is wrong. 
    std::string format = "%Y-%m-%d %H:%M:%S";
    date::sys_seconds tm_object{};
    std::istringstream input(date);        
    input >> date::parse(format, tm_object);
    if (input.fail()) 
    {
        std::cout << "Parsing failed!";
    }
    else
    {
        std::cout << "Parsing ok!\n";
        date::year_month_day ymd = date::floor<date::days>(tm_object);
        std::cout << "Day is : " << ymd.day();
    }
}

输出：

Parsing failed!

该库也可用于g ++ 5.4.0和clang。

This library also works with g++ 5.4.0 and clang.

您还可以将格式简化为％F％T ，它可以如果需要，也可以以亚秒精度工作。

You can also simplify your format down to "%F %T", and it can also work with subsecond precision if desired.

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