字典的关键性能

Question

string键是否比int键中的键更快Dictionary<,>？

Answer 1

首先,Dictionary[UPDATED]使用密钥的哈希码在其内部存储中找到它们 - 而不是密钥.而Hashcode是一个int.对int,它是正义的价值int,对于string它产生.

因此,使用int是稍快.

事实上,为字符串生成哈希代码是一个相当复杂的过程(使用Reflector的代码段)[ 希望这不作为版权漏洞,因为它不是 ]:

fixed (char* str = ((char*) this))
{
    char* chPtr = str;
    int num = 0x15051505;
    int num2 = num;
    int* numPtr = (int*) chPtr;
    for (int i = this.Length; i > 0; i -= 4)
    {
        num = (((num << 5) + num) + (num >> 0x1b)) ^ numPtr[0];
        if (i <= 2)
        {
            break;
        }
        num2 = (((num2 << 5) + num2) + (num2 >> 0x1b)) ^ numPtr[1];
        numPtr += 2;
    }
    return (num + (num2 * 0x5d588b65));
}

Answer 2

我知道这已经很老了并且回答了问题,所以这个答案适用于将来寻找它的每个人.对我来说这是一个有趣的问题,我试图找到这个问题的实际答案,结果非常有趣.

通常String作为键比作为键要慢得多.

码:

class Program
{
    object obj = new object();

    Dictionary<long, object> longDict = new Dictionary<long, object>();
    Dictionary<string, object> stringDict = new Dictionary<string, object>();

    public static void Main(string[] args)
    {
        Program hash = new Program();

        hash.Test(1000);
        hash.Test(10000);
        hash.Test(100000);
        hash.Test(1000000);
        hash.Test(10000000);

        Console.Read();
    }

    private void Test(int iterations)
    {
        Console.WriteLine(String.Format("Test for {0} iterations", iterations));

        longDict.Clear();
        stringDict.Clear();

        for (int i = 0; i < iterations; i++)
        {
            longDict.Add(i, obj);
        }

        for (int i = 0; i < iterations; i++)
        {
            stringDict.Add(i.ToString(), obj);
        }

        IntTest(iterations);
        StringTest(iterations);
    }

    private void IntTest(int iteraions)
    {
        System.Diagnostics.Stopwatch stopwatch = new System.Diagnostics.Stopwatch();
        stopwatch.Start();

        object test;

        for (int i = 0; i < iteraions; i++) {
            test = longDict[i];
        }

        stopwatch.Stop();
        Console.WriteLine("Time elapsed: {0}", stopwatch.Elapsed);
    }

    private void StringTest(int iteraions)
    {
        System.Diagnostics.Stopwatch stopwatch = new System.Diagnostics.Stopwatch();
        stopwatch.Start();

        object test;

        for (int i = 0; i < iteraions; i++)
        {
            test = stringDict[i.ToString()];
        }

        stopwatch.Stop();
        Console.WriteLine("Time elapsed: {0}", stopwatch.Elapsed);
    }
}

结果: