有人會認爲在GUID的字節數的分佈是隨機的,或者至少是非常平坦。那是什麼Guid.NewGuid總是讓GUID的
包含一個4的原因嗎?
其字符串表示包含4?爲什麼Guid.NewGuid從來沒有產生GUID,它不包含4?
即
Guid.NewGuid()。的ToString( 「N」)。包含( 「4」)
是總是如此。
快速測試表明,發生在的GUID約85%,最字節,但發生在100%4。也許這沒關係,但我很想知道爲什麼。
[編輯]
我不是非常清楚,所以編輯,以提高我的問題的清晰度。
運行此操作。不完全是深刻的,但有趣。
using System; using System.Diagnostics;
namespace ConsoleApplication1 { class Program { static bool paused, exit;
static void Main(string[] args)
{
Console.WindowHeight = (int)(0.8*Console.LargestWindowHeight);
var reportInterval = TimeSpan.FromSeconds(0.15);
WriteLine(ConsoleColor.White, "X key to exit.");
Guid guid;
byte[] bytes;
long guidCount = 0;
var counts = new long[256];
var watch = Stopwatch.StartNew();
var cursorPos = new CursorLocation();
while (!exit)
{
if (!paused)
{
guid = Guid.NewGuid();
bytes = guid.ToByteArray();
++guidCount;
for (int i = 0; i < 16; i++)
{
var b = bytes[i];
++counts[b];
}
if (watch.Elapsed > reportInterval)
{
cursorPos.MoveCursor();
DumpFrequencies(counts, guidCount);
watch.Restart();
}
}
if (Console.KeyAvailable)
{
ProcessKey(Console.ReadKey());
}
}
}
static void ProcessKey(ConsoleKeyInfo keyInfo)
{
switch (keyInfo.Key)
{
case ConsoleKey.P:
paused = !paused;
break;
case ConsoleKey.X:
exit = true;
break;
}
}
static void DumpFrequencies(long[] byteCounts, long guidCount)
{
Write("\r\n{0} GUIDs generated. Frequencies:\r\n\r\n", guidCount);
const int itemWidth = 9;
int colCount = Console.WindowWidth/(itemWidth*2);
for (int i = 0; i < 256; i++)
{
var f = (double)byteCounts[i]/(16 * guidCount);
Write(RightAdjust(itemWidth, "{0:x}", i));
Write(GetFrequencyColor(f), " {0:p}".PadRight(itemWidth), f);
if ((i + 1) % colCount == 0) Write("\r\n");
}
}
static ConsoleColor GetFrequencyColor(double f)
{
if (f < 0.003) return ConsoleColor.DarkRed;
if (f < 0.004) return ConsoleColor.Green;
if (f < 0.005) return ConsoleColor.Yellow;
return ConsoleColor.White;
}
static string RightAdjust(int w, string s, params object[] args)
{
if (args.Length > 0)
s = string.Format(s, args);
return s.PadLeft(w);
}
#region From my library, so I need not include that here...
class CursorLocation
{
public int X, Y;
public CursorLocation()
{
X = Console.CursorLeft;
Y = Console.CursorTop;
}
public void MoveCursor()
{
Console.CursorLeft = X;
Console.CursorTop = Y;
}
}
static public void Write(string s, params object[] args)
{
if (args.Length > 0) s = string.Format(s, args);
Console.Write(s);
}
static public void Write(ConsoleColor c, string s, params object[] args)
{
var old = Console.ForegroundColor;
Console.ForegroundColor = c;
Write(s, args);
Console.ForegroundColor = old;
}
static public void WriteNewline(int count = 1)
{
while (count-- > 0) Console.WriteLine();
}
static public void WriteLine(string s, params object[] args)
{
Write(s, args);
Console.Write(Environment.NewLine);
}
static public void WriteLine(ConsoleColor c, string s, params object[] args)
{
Write(c, s, args);
Console.Write(Environment.NewLine);
}
#endregion
}
}
我需要學習如何有一天格式化的東西正確這裏。 Stackoverflow是grrr吃。
[GUID是不是隨機](http://en.wikipedia.org/wiki/GUID#Algorithm)。 – 2012-03-08 14:25:50
@KonradRudolph這就是爲什麼我是如此具體的關於是隨機**或**至少是非常平坦的字節_distribution_。我知道他們不是很隨意,但不是爲什麼。 – 2012-03-08 15:11:33
停止燃燒我們的指導! – U1199880 2013-01-08 17:38:04