为什么 DateTime.ParseExact() 不能解析“9/1/2009"?使用“M/d/yyyy"

问题描述

我有一个看起来像这样的字符串:9/1/2009".我想将其转换为 DateTime 对象(使用 C#).

I have a string that looks like this: "9/1/2009". I want to convert it to a DateTime object (using C#).

这有效:

DateTime.Parse("9/1/2009", new CultureInfo("en-US"));

但我不明白为什么这不起作用:

But I don't understand why this doesn't work:

DateTime.ParseExact("9/1/2009", "M/d/yyyy", null);

日期中没有字词(例如September")，而且我知道具体的格式，所以我宁愿使用 ParseExact(我不明白为什么需要 CultureInfo).但我不断收到可怕的字符串未被识别为有效的日期时间"异常.

There's no word in the date (like "September"), and I know the specific format, so I'd rather use ParseExact (and I don't see why CultureInfo would be needed). But I keep getting the dreaded "String was not recognized as a valid DateTime" exception.

谢谢

一点点跟进.以下是 3 种有效的方法:

A little follow up. Here are 3 approaches that work:

DateTime.ParseExact("9/1/2009", "M'/'d'/'yyyy", null);
DateTime.ParseExact("9/1/2009", "M/d/yyyy", CultureInfo.InvariantCulture);
DateTime.Parse("9/1/2009", new CultureInfo("en-US"));

这里有 3 个不起作用:

And here are 3 that don't work:

DateTime.ParseExact("9/1/2009", "M/d/yyyy", CultureInfo.CurrentCulture);
DateTime.ParseExact("9/1/2009", "M/d/yyyy", new CultureInfo("en-US"));
DateTime.ParseExact("9/1/2009", "M/d/yyyy", null);

所以，Parse() 可用于en-US"，但不能用于 ParseExact...出乎意料?

So, Parse() works with "en-US", but not ParseExact... Unexpected?

推荐答案

我怀疑问题在于格式字符串中的斜杠与数据中的斜杠.这是格式字符串中区分区域性的日期分隔符，最后一个参数 null 表示使用当前区域性".如果您要么转义斜线(M'/'d'/'yyyy")或您指定CultureInfo.InvariantCulture，它将是好的.

I suspect the problem is the slashes in the format string versus the ones in the data. That's a culture-sensitive date separator character in the format string, and the final argument being null means "use the current culture". If you either escape the slashes ("M'/'d'/'yyyy") or you specify CultureInfo.InvariantCulture, it will be okay.

如果有人有兴趣复制这个:

If anyone's interested in reproducing this:

// Works
DateTime dt = DateTime.ParseExact("9/1/2009", "M'/'d'/'yyyy",
                                  new CultureInfo("de-DE"));

// Works
DateTime dt = DateTime.ParseExact("9/1/2009", "M/d/yyyy",
                                  new CultureInfo("en-US"));

// Works
DateTime dt = DateTime.ParseExact("9/1/2009", "M/d/yyyy",
                                  CultureInfo.InvariantCulture);

// Fails
DateTime dt = DateTime.ParseExact("9/1/2009", "M/d/yyyy",
                                  new CultureInfo("de-DE"));

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