What's the deal with char.GetNumericValue?

Question

I was working on Project Euler 40, and was a bit bothered that there was no int.Parse(char). Not a big deal, but I did some asking around and someone suggested char.GetNumericValue. GetNumericValue seems like a very odd method to me:

• Takes in a char as a parameter and returns...a double?
• Returns -1.0 if the char is not '0' through '9'

So what's the reasoning behind this method, and what purpose does returning a double serve? I even fired up Reflector and looked at InternalGetNumericValue, but it's just like watching Lost: every answer just leads to another question.

Answer 1

Remember that it's taking a Unicode character and returning a value. '0' through '9' are the standard decimal digits, however there are other Unicode characters that represent numbers, some of which are floating point.

Like this character: ¼

Console.WriteLine( char.GetNumericValue( '¼' ) );

Outputs 0.25 in the console window.

Answer 2

Here is a comprehensive list of actual numeric values that are returned:

0 - 0   1 - 1   2 - 2   3 - 3   4 - 4   5 - 5   6 - 6   7 - 7   8 - 8   9 - 9   
² - 2   ³ - 3   ¹ - 1   ¼ - 0.25    ½ - 0.5 ¾ - 0.75    ٠ - 0   ١ - 1   ٢ - 2   ٣ - 3   
٤ - 4   ٥ - 5   ٦ - 6   ٧ - 7   ٨ - 8   ٩ - 9   ۰ - 0   ۱ - 1   ۲ - 2   ۳ - 3   
۴ - 4   ۵ - 5   ۶ - 6   ۷ - 7   ۸ - 8   ۹ - 9   ߀ - 0   ߁ - 1   ߂ - 2   ߃ - 3   
߄ - 4   ߅ - 5   ߆ - 6   ߇ - 7   ߈ - 8   ߉ - 9   ० - 0   १ - 1   २ - 2   ३ - 3   
४ - 4   ५ - 5   ६ - 6   ७ - 7   ८ - 8   ९ - 9   ০ - 0   ১ - 1   ২ - 2   ৩ - 3   
৪ - 4   ৫ - 5   ৬ - 6   ৭ - 7   ৮ - 8   ৯ - 9   ৴ - 1   ৵ - 2   ৶ - 3   ৷ - 4   
৹ - 16  ੦ - 0   ੧ - 1   ੨ - 2   ੩ - 3   ੪ - 4   ੫ - 5   ੬ - 6   ੭ - 7   ੮ - 8   
੯ - 9   ૦ - 0   ૧ - 1   ૨ - 2   ૩ - 3   ૪ - 4   ૫ - 5   ૬ - 6   ૭ - 7   ૮ - 8   
૯ - 9   ୦ - 0   ୧ - 1   ୨ - 2   ୩ - 3   ୪ - 4   ୫ - 5   ୬ - 6   ୭ - 7   ୮ - 8   
୯ - 9   ௦ - 0   ௧ - 1   ௨ - 2   ௩ - 3   ௪ - 4   ௫ - 5   ௬ - 6   ௭ - 7   ௮ - 8   
௯ - 9   ௰ - 10  ௱ - 100 ௲ - 1000    ౦ - 0   ౧ - 1   ౨ - 2   ౩ - 3   ౪ - 4   ౫ - 5   
౬ - 6   ౭ - 7   ౮ - 8   ౯ - 9   ೦ - 0   ೧ - 1   ೨ - 2   ೩ - 3   ೪ - 4   ೫ - 5   
೬ - 6   ೭ - 7   ೮ - 8   ೯ - 9   ൦ - 0   ൧ - 1   ൨ - 2   ൩ - 3   ൪ - 4   ൫ - 5   
൬ - 6   ൭ - 7   ൮ - 8   ൯ - 9   ๐ - 0   ๑ - 1   ๒ - 2   ๓ - 3   ๔ - 4   ๕ - 5   
๖ - 6   ๗ - 7   ๘ - 8   ๙ - 9   ໐ - 0   ໑ - 1   ໒ - 2   ໓ - 3   ໔ - 4   ໕ - 5   
໖ - 6   ໗ - 7   ໘ - 8   ໙ - 9   ༠ - 0   ༡ - 1   ༢ - 2   ༣ - 3   ༤ - 4   ༥ - 5   
༦ - 6   ༧ - 7   ༨ - 8   ༩ - 9   ༪ - 0.5 ༫ - 1.5 ༬ - 2.5 ༭ - 3.5 ༮ - 4.5 ༯ - 5.5 
༰ - 6.5 ༱ - 7.5 ༲ - 8.5 ༳ - -0.5    ၀ - 0   ၁ - 1   ၂ - 2   ၃ - 3   ၄ - 4   ၅ - 5   
၆ - 6   ၇ - 7   ၈ - 8   ၉ - 9   ፩ - 1   ፪ - 2   ፫ - 3   ፬ - 4   ፭ - 5   ፮ - 6   
፯ - 7   ፰ - 8   ፱ - 9   ፲ - 10  ፳ - 20  ፴ - 30  ፵ - 40  ፶ - 50  ፷ - 60  ፸ - 70  
፹ - 80  ፺ - 90  ፻ - 100 ፼ - 10000   ᛮ - 17  ᛯ - 18  ᛰ - 19  ០ - 0   ១ - 1   ២ - 2   
៣ - 3   ៤ - 4   ៥ - 5   ៦ - 6   ៧ - 7   ៨ - 8   ៩ - 9   ៰ - 0   ៱ - 1   ៲ - 2   
៳ - 3   ៴ - 4   ៵ - 5   ៶ - 6   ៷ - 7   ៸ - 8   ៹ - 9   ᠐ - 0   ᠑ - 1   ᠒ - 2   
᠓ - 3   ᠔ - 4   ᠕ - 5   ᠖ - 6   ᠗ - 7   ᠘ - 8   ᠙ - 9   ᥆ - 0   ᥇ - 1   ᥈ - 2   
᥉ - 3   ᥊ - 4   ᥋ - 5   ᥌ - 6   ᥍ - 7   ᥎ - 8   ᥏ - 9   ᧐ - 0   ᧑ - 1   ᧒ - 2   
᧓ - 3   ᧔ - 4   ᧕ - 5   ᧖ - 6   ᧗ - 7   ᧘ - 8   ᧙ - 9   ᭐ - 0   ᭑ - 1   ᭒ - 2   
᭓ - 3   ᭔ - 4   ᭕ - 5   ᭖ - 6   ᭗ - 7   ᭘ - 8   ᭙ - 9   ⁰ - 0   ⁴ - 4   ⁵ - 5   
⁶ - 6   ⁷ - 7   ⁸ - 8   ⁹ - 9   ₀ - 0   ₁ - 1   ₂ - 2   ₃ - 3   ₄ - 4   ₅ - 5   
₆ - 6   ₇ - 7   ₈ - 8   ₉ - 9   ⅓ - 0.333333333333333   ⅔ - 0.666666666666667   ⅕ - 0.2 ⅖ - 0.4 ⅗ - 0.6 ⅘ - 0.8 
⅙ - 0.166666666666667   ⅚ - 0.833333333333333   ⅛ - 0.125   ⅜ - 0.375   ⅝ - 0.625   ⅞ - 0.875   ⅟ - 1   Ⅰ - 1   Ⅱ - 2   Ⅲ - 3   
Ⅳ - 4   Ⅴ - 5   Ⅵ - 6   Ⅶ - 7   Ⅷ - 8   Ⅸ - 9   Ⅹ - 10  Ⅺ - 11  Ⅻ - 12  Ⅼ - 50  
Ⅽ - 100 Ⅾ - 500 Ⅿ - 1000    ⅰ - 1   ⅱ - 2   ⅲ - 3   ⅳ - 4   ⅴ - 5   ⅵ - 6   ⅶ - 7   
ⅷ - 8   ⅸ - 9   ⅹ - 10  ⅺ - 11  ⅻ - 12  ⅼ - 50  ⅽ - 100 ⅾ - 500 ⅿ - 1000    ↀ - 1000    
ↁ - 5000    ↂ - 10000   ① - 1   ② - 2   ③ - 3   ④ - 4   ⑤ - 5   ⑥ - 6   ⑦ - 7   ⑧ - 8   
⑨ - 9   ⑩ - 10  ⑪ - 11  ⑫ - 12  ⑬ - 13  ⑭ - 14  ⑮ - 15  ⑯ - 16  ⑰ - 17  ⑱ - 18  
⑲ - 19  ⑳ - 20  ⑴ - 1   ⑵ - 2   ⑶ - 3   ⑷ - 4   ⑸ - 5   ⑹ - 6   ⑺ - 7   ⑻ - 8   
⑼ - 9   ⑽ - 10  ⑾ - 11  ⑿ - 12  ⒀ - 13  ⒁ - 14  ⒂ - 15  ⒃ - 16  ⒄ - 17  ⒅ - 18  
⒆ - 19  ⒇ - 20  ⒈ - 1   ⒉ - 2   ⒊ - 3   ⒋ - 4   ⒌ - 5   ⒍ - 6   ⒎ - 7   ⒏ - 8   
⒐ - 9   ⒑ - 10  ⒒ - 11  ⒓ - 12  ⒔ - 13  ⒕ - 14  ⒖ - 15  ⒗ - 16  ⒘ - 17  ⒙ - 18  
⒚ - 19  ⒛ - 20  ⓪ - 0   ⓫ - 11  ⓬ - 12  ⓭ - 13  ⓮ - 14  ⓯ - 15  ⓰ - 16  ⓱ - 17  
⓲ - 18  ⓳ - 19  ⓴ - 20  ⓵ - 1   ⓶ - 2   ⓷ - 3   ⓸ - 4   ⓹ - 5   ⓺ - 6   ⓻ - 7   
⓼ - 8   ⓽ - 9   ⓾ - 10  ⓿ - 0   ❶ - 1   ❷ - 2   ❸ - 3   ❹ - 4   ❺ - 5   ❻ - 6   
❼ - 7   ❽ - 8   ❾ - 9   ❿ - 10  ➀ - 1   ➁ - 2   ➂ - 3   ➃ - 4   ➄ - 5   ➅ - 6   
➆ - 7   ➇ - 8   ➈ - 9   ➉ - 10  ➊ - 1   ➋ - 2   ➌ - 3   ➍ - 4   ➎ - 5   ➏ - 6   
➐ - 7   ➑ - 8   ➒ - 9   ➓ - 10  ⳽ - 0.5 〇 - 0   〡 - 1   〢 - 2   〣 - 3   〤 - 4   
〥 - 5   〦 - 6   〧 - 7   〨 - 8   〩 - 9   〸 - 10  〹 - 20  〺 - 30  ㆒ - 1   ㆓ - 2   
㆔ - 3   ㆕ - 4   ㈠ - 1   ㈡ - 2   ㈢ - 3   ㈣ - 4   ㈤ - 5   ㈥ - 6   ㈦ - 7   ㈧ - 8   
㈨ - 9   ㈩ - 10  ㉑ - 21  ㉒ - 22  ㉓ - 23  ㉔ - 24  ㉕ - 25  ㉖ - 26  ㉗ - 27  ㉘ - 28  
㉙ - 29  ㉚ - 30  ㉛ - 31  ㉜ - 32  ㉝ - 33  ㉞ - 34  ㉟ - 35  ㊀ - 1   ㊁ - 2   ㊂ - 3   
㊃ - 4   ㊄ - 5   ㊅ - 6   ㊆ - 7   ㊇ - 8   ㊈ - 9   ㊉ - 10  ㊱ - 36  ㊲ - 37  ㊳ - 38  
㊴ - 39  ㊵ - 40  ㊶ - 41  ㊷ - 42  ㊸ - 43  ㊹ - 44  ㊺ - 45  ㊻ - 46  ㊼ - 47  ㊽ - 48  
㊾ - 49  ㊿ - 50  ０ - 0   １ - 1   ２ - 2   ３ - 3   ４ - 4   ５ - 5   ６ - 6   ７ - 7   
８ - 8   ９ - 9