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【笨問題】C# 字串依 ASCII 排序

 1 year ago
source link: https://blog.darkthread.net/blog/cs-str-orderby-ascii/
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【笨問題】C# 字串依 ASCII 排序

calendar.svg 2022-10-11 08:16 PM comment.svg 0 eye.svg 350

許多程式老骨腦袋都有這麼一張表，並且會背幾組特別數字：空白鍵是 32 (0x20)，0 是 48 (0x30)、A 是 65 (0x41)，加 32 可以變成 a 97 (0x61)...

Fig1_638010877292973018.png
圖片來源：維基百科

在 C# 做字串排序，一時恍忽，熊熊覺得 new[] { "Jeffrey","darkthread", } 排序 "J"effrey (ASCII 0x4a) 應該要排在 "d"arkthread (0x64) 前面，但事實不然：

Fig3_638010877294881060.png

猛然想起，.NET 字串排序先後是由 CultureInfo 決定，誰跟你 ASCII？(延伸閱讀：.NET 中文字串排序(筆劃、注音))

那... 如果我要依 ASCII 排序怎麼辦？請用 StringComparer.Ordinal，它還有個兄弟叫 StringComparer.OrdinalIgnoreCase，一樣依 ASCII，但不分大小寫，a 在 B 前面，A 在 a 前面。

寫段程式實測驗證：

void Main()
{
    var array = new[] { "0", "a", "b", "A", "B" };
	Action<IEnumerable<string>, string> dump = (a, n) => {
		Console.WriteLine(n);
		Console.WriteLine(new string('=', 36));
		Console.WriteLine(string.Join(" < ", a.ToArray()));
		Console.WriteLine();
	};
    
    dump(array, "Raw");
    Array.Sort(array);
    dump(array, "Sort");
    dump(array.OrderBy(o => o), "OrderBy");
    Array.Sort(array, StringComparer.Ordinal);
    dump(array, "Sort StringComparer.Ordinal");
    dump(array.OrderBy(o => o, StringComparer.Ordinal), 
		"OrderBy StringComparer.Ordinal");
	Array.Sort(array, StringComparer.OrdinalIgnoreCase);
	dump(array, "Sort StringComparer.OrdinalIgnoreCase");
}

Fig2_638010877296941874.png

打完收工。

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