DateTime.TryParseExact未正常工作 [英] DateTime.TryParseExact not working as expected

问题描述

任何人都可以解释为什么下面的代码片段返回true？

Can anyone explain why the following snippet returns true?

根据文档的的中的d自定义格式说明，一个单一的数字一天不带前导零的格式。那么，为什么不TryParseExact时，我给它一个个位数的一天，一个前导零

According to the docs for The "d" custom format specifier, "A single-digit day is formatted without a leading zero." So why doesn't TryParseExact fail when I give it a single-digit day with a leading zero?

DateTime x;
return DateTime.TryParseExact
(
    "01/01/2001",
    @"d\/MM\/yyyy",
    null,
    System.Globalization.DateTimeStyles.None,
    out x
);

更新

我想，也许我还不清楚最初。我真的很想要知道的就是：为什么TryParseExact所有我看到的文档接受不完全匹配一些值，'D'匹配'01'和'1'是一样多，如果'MM'匹配三八以及03的错误。 这里的问题不说，价值观是等价的，它是不匹配的格式。

I think maybe I was unclear originally. What I am really trying to get at is: Why does TryParseExact accept some values that don't match exactly? from all of the documentation I have seen, 'd' matching '01' and '1' is just as much a bug as if 'MM' matched 'March' as well as '03'. The issue here isn't that the values are equivalent, its that they don't match the format.

文件的有关片段是

• 从的 TryParseExact ：字符串表示的格式必须指定格式完全相同

通过的'D'说明：单数字的日期格式没有前导零。

这似乎非常清楚，我认为'01'具有领先的0的，因此不完全匹配'D'。

It seems abundantly clear to me that '01' has a leading 0, and therefore doesn't exactly match 'd'.

推荐答案

从.NET 4源DateTimeParse.ParseByFormat（）：

From the .NET 4 source in DateTimeParse.ParseByFormat():

case 'd':
    // Day & Day of week 
    tokenLen = format.GetRepeatCount();
    if (tokenLen <= 2) { 
        // "d" & "dd" 

        if (!ParseDigits(ref str, tokenLen, out tempDay)) { 
            if (!parseInfo.fCustomNumberParser ||
                !parseInfo.parseNumberDelegate(ref str, tokenLen, out tempDay)) {

                result.SetFailure(ParseFailureKind.Format, "Format_BadDateTime", null);
                return (false); 
            }
        } 
        if (!CheckNewValue(ref result.Day, tempDay, ch, ref result)) { 
            return (false);
        }
    }
    else
    {...}

解析器肿块D和DD在一起。

The parser lumps "d" and "dd" together.

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