問題描述

我經(jīng)常使用字符.IsDigit 來檢查 char 是否是一個數(shù)字，這在 LINQ 查詢中特別方便以預(yù)先檢查 int.Parse 如下:"123".All(Char.IsDigit).

但是有些字符是數(shù)字，但不能像 ? 那樣解析為 int.

//真bool isDigit = Char.IsDigit('?');var文化 = CultureInfo.GetCultures(CultureTypes.SpecificCultures);整數(shù);//錯誤的bool isIntForAnyCulture = 文化.Any(c => int.TryParse('?'.ToString(), NumberStyles.Any, c, out num));

這是為什么?我的 int.Parse-通過 Char.IsDigit 進行預(yù)檢查是否不正確?

有 310 個字符是數(shù)字:

ListdigitList = Enumerable.Range(0, UInt16.MaxValue).Select(i => Convert.ToChar(i)).Where(c => Char.IsDigit(c)).ToList();

以下是 .NET 4 (ILSpy) 中 Char.IsDigit 的實現(xiàn):

public static bool IsDigit(char c){如果 (char.IsLatin1(c)){返回 c >= '0' &&c <= '9';}返回 CharUnicodeInfo.GetUnicodeCategory(c) == UnicodeCategory.DecimalDigitNumber;}

那么為什么會有屬于 DecimalDigitNumber-category("十進制數(shù)字字符，即 0 到 9 范圍內(nèi)的字符...")在任何文化中都不會被解析為 int 嗎?

這是因為它正在檢查 Unicode數(shù)字，十進制數(shù)字"類別中的所有數(shù)字，如下所列:

http://www.fileformat.info/info/unicode/類別/Nd/list.htm

這并不意味著它是當前語言環(huán)境中的有效數(shù)字字符.事實上，使用int.Parse()，你只能解析正常的英文數(shù)字，??而不管區(qū)域設(shè)置如何.

例如，這不起作用:

int test = int.Parse("?", CultureInfo.GetCultureInfo("ar"));

即使 ? 是有效的阿拉伯數(shù)字字符，并且ar"是阿拉伯語區(qū)域設(shè)置標識符.

Microsoft 文章 如何:解析 Unicode 數(shù)字" 指出那個:

.NET Framework 解析為十進制的唯一 Unicode 數(shù)字是 ASCII 數(shù)字 0 到 9，由代碼值 U+0030 到 U+0039 指定..NET Framework 將所有其他 Unicode 數(shù)字解析為字符.

但是，請注意，您可以使用 char.GetNumericValue() 將 unicode 數(shù)字字符轉(zhuǎn)換為雙精度數(shù)字.

返回值是 double 而不是 int 的原因是這樣的:

Console.WriteLine(char.GetNumericValue('?'));//打印 0.25

您可以使用類似的方法將字符串中的所有數(shù)字字符轉(zhuǎn)換為它們的 ASCII 等價物:

public string ConvertNumericChars(string input){StringBuilder 輸出 = new StringBuilder();foreach(輸入中的字符ch){如果 (char.IsDigit(ch)){雙值 = char.GetNumericValue(ch);if ((value >= 0) && (value <= 9) && (value == (int)value)){output.Append((char)('0'+(int)value));繼續(xù);}}output.Append(ch);}返回 output.ToString();}

I often use Char.IsDigit to check if a char is a digit which is especially handy in LINQ queries to pre-check int.Parse as here: "123".All(Char.IsDigit).

But there are chars which are digits but which can't be parsed to int like ?.

// true
bool isDigit = Char.IsDigit('?'); 

var cultures = CultureInfo.GetCultures(CultureTypes.SpecificCultures);
int num;
// false
bool isIntForAnyCulture = cultures
    .Any(c => int.TryParse('?'.ToString(), NumberStyles.Any, c, out num)); 

Why is that? Is my int.Parse-precheck via Char.IsDigit thus incorrect?

There are 310 chars which are digits:

List<char> digitList = Enumerable.Range(0, UInt16.MaxValue)
   .Select(i => Convert.ToChar(i))
   .Where(c => Char.IsDigit(c))
   .ToList(); 

Here's the implementation of Char.IsDigit in .NET 4 (ILSpy):

public static bool IsDigit(char c)
{
    if (char.IsLatin1(c))
    {
        return c >= '0' && c <= '9';
    }
    return CharUnicodeInfo.GetUnicodeCategory(c) == UnicodeCategory.DecimalDigitNumber;
}

So why are there chars that belong to the DecimalDigitNumber-category("Decimal digit character, that is, a character in the range 0 through 9...") which can't be parsed to an int in any culture?

It's because it is checking for all digits in the Unicode "Number, Decimal Digit" category, as listed here:

http://www.fileformat.info/info/unicode/category/Nd/list.htm

It doesn't mean that it is a valid numeric character in the current locale. In fact using int.Parse(), you can ONLY parse the normal English digits, regardless of the locale setting.

For example, this doesn't work:

int test = int.Parse("?", CultureInfo.GetCultureInfo("ar"));

Even though ? is a valid Arabic digit character, and "ar" is the Arabic locale identifier.

The Microsoft article "How to: Parse Unicode Digits" states that:

The only Unicode digits that the .NET Framework parses as decimals are the ASCII digits 0 through 9, specified by the code values U+0030 through U+0039. The .NET Framework parses all other Unicode digits as characters.

However, note that you can use char.GetNumericValue() to convert a unicode numeric character to its numeric equivalent as a double.

The reason the return value is a double and not an int is because of things like this:

Console.WriteLine(char.GetNumericValue('?')); // Prints 0.25

You could use something like this to convert all numeric characters in a string into their ASCII equivalent:

public string ConvertNumericChars(string input)
{
    StringBuilder output = new StringBuilder();

    foreach (char ch in input)
    {
        if (char.IsDigit(ch))
        {
            double value = char.GetNumericValue(ch);

            if ((value >= 0) && (value <= 9) && (value == (int)value))
            {
                output.Append((char)('0'+(int)value));
                continue;
            }
        }

        output.Append(ch);
    }

    return output.ToString();
}

這篇關(guān)于為什么 Char.IsDigit 對于無法解析為 int 的字符返回 true?的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網(wǎng)！